Peptide analogues of GIP for treatment of diabetes, insulin resistance and obesity

ABSTRACT

The present invention provides peptide analogues which are antagonists of gastric inhibitory peptide (GIP). The peptides, based on GIP 1-42 include substitutions and/or modifications which have enhanced resistance to degradation by the enzyme dipeptidyl peptidase IV (DPP IV). The invention also provides a process of N terminally modifying GIP and the use of the peptide analogues for treatment of diabetes.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part application of InternationalApplication No. PCT/GB2005/000710, which was filed on Feb. 25, 2005,designated the United States and was published in English, which claimsbenefit of U.K. Application No. GB 0404124.0, filed on Feb. 25, 2004.The present application is also a continuation-in-part of U.S.application Ser. No. 09/937,687, filed Jan. 8, 2002, which is the U.S.National Phase Application of International Application No.PCT/GB00/01089, which is designated the United States and was filed onMar. 29, 2000 and published in English, which in turn claims the benefitof GB9907216.7, filed on Mar. 29, 1999, and GB9917565.5, filed Jul. 27,1999. The entire teachings of the above applications are incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention relates to the release of insulin and the controlof blood glucose concentration. More particularly the invention relatesto antagonists of gastric inhibitory peptide (GIP) as pharmaceuticalpreparations for treatment of type 2 diabetes.

BACKGROUND

Obesity and diabetes are predicted to reach epidemic proportionsthroughout the world in the next 20 years and current treatments do notrestore normal insulin sensitivity or glucose homeostasis, thereinresulting in debilitating diabetic complications and premature death.

Gastric inhibitory polypeptide (GIP) and glucagon-likepeptide-1(7-36)amide (truncated GLP-1; tGLP-1) are two importantinsulin-releasing hormones secreted from endocrine cells in theintestinal tract in response to feeding. Together with autonomic nervesthey play a vital supporting role to the pancreatic islets in thecontrol of blood glucose homeostasis and nutrient metabolism.

GIP is released from intestinal endocrine K-cells into the bloodstreamfollowing ingestion of carbohydrate, protein and particularly fat(Meier, J. J. et al., 2002, Regul. Pept. 107:1-13). GIP was initiallydiscovered through its ability to inhibit gastric acid secretion (Brown,J. C. et al. 1969, Can. J. Physiol. Pharmacol. 47:113-114) but its majorphysiological role is now generally believed to be that of an incretinhormone that targets pancreatic islets to enhance insulin secretion andhelp reduce postprandial hyperglycemia (Creutzfeldt, W., 2001, Exp.Clin. Endocrinol. Diabetes 109:S288-S303). GIP acts through binding tospecific G-protein coupled GIP receptors located on pancreaticbeta-cells (Wheeler, M. B. et al., 1995, Endocrinology 136:4629-4639).Like its sister incretin hormone, glucagon-like peptide-1 (GLP-1), thisability to stimulate insulin secretion plus other potentially beneficialactions on pancreatic beta-cell growth and differentiation have led tomuch interest in using GIP or GLP-1 receptor agonists in the treatmentof type 2 diabetes (Creutzfeldt, W., 2001, Exp. Clin. Endocrinol.Diabetes 109:S288-S303; Holz, G. G. et al., 2003, Curr. Med. Chem.10:2471-2483).

Since GIP functions as a potent and natural stimulator of insulinsecretion released from the intestine by feeding, it is widely expectedthat antagonists opposing GIP action will block the insulin-releasingactions of GIP and impair both oral glucose tolerance and the glycemicresponse to nutrient ingestion. In fact, all studies published to dateindicate that GIP is a key physiological component of the enteroinsularaxis and that functional ablation of GIP leads to impaired glucosehomeostasis moving the metabolic characteristic towards a type 2diabetes phenotype (Gault, V. A. et al., 2002, Biochem. Biophys. Res.Commun. 290:1420-1426).

Dipeptidyl peptidase IV (DPP IV; EC 3.4.14.5) has been identified as akey enzyme responsible for inactivation of GIP and tGLP-1 in serum. Thisoccurs through the rapid removal of the N-terminal dipeptides Tyr¹-Ala²and His⁷-Ala⁸ giving rise to the main metabolites GIP(3-42) andGLP-1(9-36)amide, respectively. These truncated peptides are reported tolack biological activity or to even serve as antagonists at GIP ortGLP-1 receptors. The resulting biological half-lives of these incretinhormones in vivo are therefore very short, estimated to be no longerthan 5 minutes. DPP IV is completely inhibited in serum by the additionof diprotin A (DPA, 0.1 mmol/l).

In situations of normal glucose regulation and pancreatic B-cellsensitivity, this short duration of action is advantageous infacilitating momentary adjustments to homeostatic control. However, thecurrent goal of a possible therapeutic role of incretin hormones,particularly tGLP-1 in non-insulin dependent diabetes (NIDDM) therapy isfrustrated by a number of factors in addition to finding a convenientroute of administration. Most notable of these are rapid peptidedegradation and rapid absorption (peak concentrations are reached in 20minutes) and the resulting need for both high dosage and precise timingwith meals. Recent therapeutic strategies have focused on precipitatedpreparations to delay peptide absorption and inhibition of GLP-1degradation using specific inhibitors of DPP IV. A possible therapeuticrole is also suggested by the observation that a specific inhibitor ofDPP IV, isoleucine thiazolidide, lowered blood glucose and enhancedinsulin secretion in glucose-treated diabetic obese Zucker ratspresumably by protecting against catabolism of the incretin hormonestGLP-1 and GIP.

Studies have indicated that tGLP-1 infusion restores pancreatic B-cellsensitivity, insulin secretory oscillations and improved glycemiccontrol in various groups of patients with impaired glucose tolerance(IGT) or NIDDM. Longer term studies also show significant benefits oftGLP-1 injections in NIDDM and possibly IDDM therapy, providing a majorincentive to develop an orally effective or long-acting tGLP-1 analogue.Several attempts have been made to produce structurally modifiedanalogues of tGLP-1 which are resistant to DPP IV degradation. Asignificant extension of serum half-life is observed with His⁷-glucitoltGLP-1 and tGLP-1 analogues substituted at position 8 with Gly, Aib(amino isobutyric acid), Ser or Thr. However, these structuralmodifications seem to impair receptor binding and insulinotrophicactivity thereby compromising part of the benefits of protection fromproteolytic degradation. In recent studies using His⁷-glucitol tGLP-1,resistance to DPP IV and serum degradation was accompanied by severeloss of insulin releasing activity.

GIP shares not only the same degradation pathway as tGLP-1 but manysimilar physiological actions, including stimulation of insulin andsomatostatin secretion, and the enhancement of glucose disposal. Theseactions are viewed as key aspects in the antihyperglycemic properties oftGLP-1, and there is therefore good expectation that GIP may havesimilar potential as NIDDM therapy. Indeed, compensation by GIP is heldto explain the modest disturbances of glucose homeostasis observed intGLP-1 knockout mice. Apart from early studies, the anti-diabeticpotential of GIP has not been explored and tGLP-1 may seem moreattractive since it is viewed by some as a more potent insulinsecretagogue when infused at so called physiological concentrationsestimated by radioimmunoassay (RIA).

There is therefore a need for a diabetes treatment that includes ananalogue of GIP which can cause release of insulin, yet also beresistant to rapid degradation by DPP IV.

SUMMARY OF THE INVENTION

Disclosed herein are GIP antagonist peptides which are resistant torapid degradation by DPP IV.

The invention includes a peptide analogue of GIP(1-42) (SEQ ID NO: 1),which includes at least 12 amino acid residues from the N-terminal endof GIP(3-42). The invention also includes a peptide analogue ofGIP(1-42) (SEQ ID NO:1), which includes at least 12 amino acid residuesfrom the N-terminal end of GIP(1-42) and having an amino acidsubstitution at Glu³.

The amino acid substituted at Glu³ can be selected from the groupconsisting of: proline, hydroxyproline, lysine, tyrosine, phenylalanineand tryptophan. Specifically, a proline can be substituted for Glu³. Thepeptide analogue can further include modification by fatty acid additionat an epsilon amino group of at least one lysine residue. The lysineresidue can be Lys¹⁶ or Lys³⁷.

The peptide analogue of GIP(1-42) (SEQ ID NO: 1) can include at least 12amino acid residues from the N-terminal end of GIP(1-42), and an aminoacid modification at amino acid residues 1, 2 or 3. The N-terminal aminoacid residue can be acetylated. It can further comprising modificationby fatty acid addition at an epsilon amino group of at least one lysineresidue. The modification can be the linking of, e.g., a C-8, a C-10, aC-12, a C-14, a C-16, a C-18 or a C-20 palmitate group to the epsilonamino group of a lysine residue. The lysine residue can be Lys¹⁶, orLys³⁷.

The invention also includes a peptide analogue of GIP(1-42) (SEQ ID NO:1), wherein the analogue comprises a base peptide consisting of one ofthe following: GIP(1-12), GIP(1-13), GIP(1-14), GIP(1-15), GIP(1-16),GIP(1-17), GIP(1-18), GIP(1-19), GIP(1-20), GIP(1-21), GIP(1-22),GIP(1-23), GIP(1-24), GIP(1-25), GIP(1-26), GIP(1-27), GIP(1-28),GIP(1-29), GIP(1-30), GIP(1-31), GIP(1-32), GIP(1-33), GIP(1-34),GIP(1-35), GIP(1-36), GIP(1-37), GIP(1-38), GIP(1-39), GIP(1-40),GIP(1-41) and GIP(1-42), where the base peptide-possesses one or more ofthe following modifications: (1) an amino acid substitution at Glu³; (2)a modification by fatty acid addition at an epsilon amino group of atleast one lysine residue; and (3) a modification by N-terminalacetylation. Such a peptide analogue can have a proline substituted forGlu³. It can also have a modification in the form of a C-16 palmitategroup linked to the epsilon amino group of a lysine residue. Themodification can be the linking of, e.g., a C-8, a C-10, a C-12, a C-14,a C-16, a C-18 or a C-20 palmitate group to the epsilon amino group of alysine residue. The lysine residue can be Lys¹⁶, or Lys³⁷.

The invention further includes a peptide analogue of GIP(1-42) (SEQ IDNO: 1), comprising at least 12 amino acid residues from the N-terminalend of GIP(3-42), wherein the peptide analogue is resistant todegradation by enzyme DPP IV when compared to naturally-occurring GIP.

Also included is a peptide analogue of GIP(1-42) (SEQ ID NO: 1),comprising at least 12 amino acid residues from the N-terminal end ofGIP(1-42) and having an amino acid substitution at Glu³, wherein thepeptide analogue is resistant to degradation by enzyme DPP IV whencompared to naturally-occurring GIP.

In addition, the invention includes a peptide analogue of GIP(1-42) (SEQID NO:1), comprising at least 12 amino acid residues from the N-terminalend of GIP(3-42), wherein the peptide analogue modulates insulinsecretion.

The invention also includes a peptide analogue of GIP(1-42) (SEQ ID NO:1), comprising at least 12 amino acid residues from the N-terminal endof GIP(1-42) and having an amino acid substitution at Glu³, wherein thepeptide analogue modulates insulin secretion.

The invention also includes use of any of the analogues in thepreparation of a medicament for the treatment of obesity, insulinresistance, insulin resistant metabolic syndrome (Syndrome X) or type 2diabetes.

The invention also includes a pharmaceutical composition including thepeptide analogues. The pharmaceutical composition can further comprise apharmaceutically acceptable carrier. The peptide analogue can be in theform of a pharmaceutically acceptable salt, or a pharmaceuticallyacceptable acid addition salt.

In a further aspect, the invention includes a method of treating insulinresistance, obesity, or type 2 diabetes, where the method comprisesadministering to a mammal in need of such treatment a therapeuticallyeffective amount of the pharmaceutical composition.

According to the present invention there is provided an effectivepeptide analogue of the biologically active GIP(1-42) which has improvedcharacteristics for treatment of Type 2 diabetes wherein the analoguecomprises at least 15 amino acid residues from the N terminus ofGIP(1-42) and has at least one amino acid substitution or modificationat position 1-3 and not including Tyr¹ glucitol GIP(1-42).

The structures of human and porcine GIP(1-42) are shown below. Theporcine peptide differs by just two amino acid substitutions atpositions 18 and 34.

The analogue may include modification by fatty acid addition at anepsilon amino group of at least one lysine residue.

The invention includes Tyr¹ glucitol GIP(1-42) having fatty acidaddition at an epsilon amino group of at least one lysine residue.

Analogues of GIP(1-42) may have an enhanced capacity to stimulateinsulin secretion, enhance glucose disposal, delay glucose absorption ormay exhibit enhanced stability in plasma as compared to native GIP. Theyalso may have enhanced resistance to degradation.

Any of these properties will enhance the potency of the analogue as atherapeutic agent.

Analogues having D-amino acid substitutions in the 1, 2 and 3 positionsand/or N-glycated, N-alkylated, N-acetylated or N-acylated amino acidsin the 1 position are resistant to degradation in vivo.

Various amino acid substitutions at second and third amino terminalresidues are included, such as GIP(1-42)Gly², GIP(142)Ser²,GIP(1-42)Abu², GIP(1-42)Aib², GIP(1-42)D-Ala², GIP(1-42)Sar², andGIP(1-42)Pro³.

Amino-terminally modified GIP analogues include N-glycated GIP(1-42),N-alkylated GIP(142), N-acetylated GIP(142), N-acetyl-GIP(1-42) andN-isopropyl GIP(1-42).

Other stabilized analogues include those with a peptide isostere bondbetween amino terminal residues at position 2 and 3. These analogues maybe resistant to the plasma enzyme dipeptidyl-peptidase IV (DPP IV) whichis largely responsible for inactivation of GIP by removal of theamino-terminal dipeptide Tyr¹-Ala².

In particular embodiments, the invention provides a peptide which ismore potent than human or porcine GIP in moderating blood glucoseexcursions, said peptide consisting of GIP(1-42) or N-terminal fragmentsof GIP(1-42) consisting of up to between 15 to 30 amino acid residuesfrom the N-terminus (i.e., GIP(1-15) GIP(1-3)) with one or moremodifications-selected from the group consisting of:

-   -   (a) substitution of Ala² by Gly;    -   (b) substitution of Ala² by Ser;    -   (c) substitution of Ala² by Abu;    -   (d) substitution of Ala² by Aib;    -   (e) substitution of Ala² by D-Ala;    -   (f) substitution of Ala² by Sar (sarcosine);    -   (g) substitution of Glu³ by Pro;    -   (h) modification of Tyr¹ by acetylation;    -   (i) modification of Tyr¹ by acylation;    -   (j) modification of Tyr¹ by alkylation;    -   (k) modification of Tyr¹ by glycation;    -   (l) conversion of Ala²-Glu³ bond to a psi [CH₂NH] bond;    -   (m) conversion of Ala²-Glu³ bond to a stable peptide isotere        bond; and    -   (n) (n-isopropyl-H) 1GIP.

The invention also provides the use of Tyr¹-glucitol GIP in thepreparation of a medicament for the treatment of diabetes.

The invention further provides improved pharmaceutical compositionsincluding analogues of GIP with improved pharmacological properties.

Other possible analogues include certain commonly encountered aminoacids, which are not encoded by the genetic code, for example,beta-alanine (beta-ala), or other omega-amino acids, such as 3-aminopropionic, 4-amino butyric and so forth, ornithine (Orn), citrulline(Cit), homoarginine (Har), t-butylalanine (t-BuA), t-butylglycine(t-BuG), N-methylisoleucine (N-MeIle), phenylglycine (Phg), andcyclohexylalanine (Cha), norleucine (Nle), cysteic acid (Cya) andmethionine sulfoxide (MSO), substitution of the D form of a neutral oracidic amino acid or the D form of tyrosine for tyrosine.

According to the present invention there is also provided apharmaceutical composition useful in the treatment of diabetes type IIwhich comprises an effective amount of the peptide as described herein,in admixture with a pharmaceutically acceptable excipient.

The invention also provides a method of N-terminally modifying GIP oranalogues thereof the method comprising the steps of synthesizing thepeptide from the C terminal to the penultimate N terminal amino acid,adding tyrosine to a bubbler system as a F-moc protected Tyr(tBu)-Wangresin, deprotecting the N-terminus of the tyrosine and reacting with themodifying agent, allowing the reaction to proceed to completion,cleaving the modified tyrosine from the Wang resin and adding themodified tyrosine to the peptide synthesis reaction.

Preferably the agent is glucose, acetic anhydride or pyroglutamic acid.

The invention will now be demonstrated with reference to the followingnon-limiting examples and the accompanying figures wherein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a illustrates degradation of GIP by DPP IV.

FIG. 1 b illustrates degradation of GIP and Tyr¹ glucitol GIP by DPP IV.

FIG. 2 a illustrates degradation of GIP human plasma.

FIG. 2 b illustrates degradation of GIP and Tyr¹ glucitol GIP by humanplasma.

FIG. 3 illustrates electrospray ionization mass spectrometry of GIP,Tyr¹-glucitol GIP and the major degradation fragment GIP(3-42).

FIG. 4 shows the effects of GIP and glycated GIP on plasma glucosehomeostasis.

FIG. 5 shows effects of GIP on plasma insulin responses.

FIG. 6 illustrates DPP-IV degradation of GOP (1-42).

FIG. 7 illustrates DPP-IV degradation of GIP (Abu²).

FIG. 8 illustrates DPP-IV degradation of GIP (Sar²).

FIG. 9 illustrates DPP-IV degradation of GIP (Ser²).

FIG. 10 illustrates DPP-IV degradation of N-Acetyl-GIP.

FIG. 10 illustrates DPP-IV degradation of glycated GIP.

FIG. 12 illustrates human plasma degradation of GIP.

FIG. 13 illustrates human plasma degradation of GIP (Abu²).

FIG. 14 illustrates human plasma degradation of GIP (Sar²).

FIG. 15 illustrates human plasma degradation of GIP (Ser²).

FIG. 16 illustrates human plasma degradation of glycated GIP.

FIG. 17 shows the effects of various concentrations of GIP 1-42 and GIP(Abu²) on insulin release from BRIN-BD11 cells incubated at 5.6 mMglucose.

FIG. 18 shows the effects of various concentrations of GIP 1-42 and GP(Abu²) on insulin release from BRIN-BD11 cells incubated at 16.7 mMglucose.

FIG. 19 shows the effects of various concentrations of GIP 1-42 and GIP(Sar²) on insulin release from BRIN-BD11 cells incubated at 5.6 mMglucose.

FIG. 20 shows the effects of various concentrations of GIP 1-42 and GIP(Ser²) on insulin release from BRIN-BD11 cells incubated at 16.7 mMglucose.

FIG. 21 shows the effects of various concentrations of GIP 1-42 and GIP(Ser²) on insulin release from BRIN-BD11 cells incubated at 5.6 mMglucose.

FIG. 22 shows the effects of various concentrations of GIP 1-42 and GIP(Ser¹) on insulin release from BRIN-BD11 cells incubated at 16.7 mMglucose.

FIG. 23 shows the effects of various concentrations of GIP 142 andN-Acetyl-GIP 1-42 on insulin release from BRIN-BD11 cells incubated at16.7M glucose.

FIG. 24 shows the effects of various concentrations of GIP 1-42 andN-Acetyl-GIP 1-42 on insulin release from BRIN-BD11 cells incubated at5.6 mM glucose.

FIG. 25 shows the effects of various concentrations of GIP 1-42 andglycated GIP 1-42 on insulin release from BRIN-BD11 cells incubated at5.6 mM glucose.

FIG. 26 shows the effects of various concentrations of GIP 1-42 andglycated GIP 1-42 on insulin release from BRIN-BD11 cells incubated at16.7 mM glucose.

FIG. 27 shows the effects of various concentrations of GIP 1-42 and GIP(Gly²) on insulin release from BRIN-BD11 cells incubated at 5.6 mMglucose.

FIG. 28 shows the effects of various concentrations of GIP 1-42 and GIP(Gly²) on insulin release from BRIN-BD11 cells incubated at 16.7 mMglucose.

FIG. 29 shows the effects of various concentrations of GIP 1-42 and GIP(Pro³) on insulin release from BRIN-BD11 cells incubated at 5.6 mMglucose.

FIG. 30 shows the effects of various concentrations of GIP 1-42 and GIP(Pro³) on insulin release from BRIN-BD11 cells incubated at 16.7 mMglucose.

FIG. 31 a shows the primary structure of human gastric inhibitorypolypeptide (GIP) (SEQ ID NO: 1), and FIG. 3 lb shows the primarystructure of porcine gastric inhibitory polypeptide (GIP) (SEQ ID NO:2).

FIGS. 32A and 32B are a line graph and a bar graph, respectively,showing the effects of (Pro³)GIP on GIP-stimulated cyclic AMP generationand insulin secretion in vitro.

FIGS. 33A-33F are a set of six bar graphs showing the effects ofGlu³-substituted forms of GIP and GIP(3-42) on GIP-stimulated insulinsecretion in vitro.

FIGS. 34A through 34D are a set of two line graphs (FIGS. 34A, 34C) andtwo bar graphs (FIGS. 34B, 34D) showing that acute administration of(Pro³)GIP completely antagonises the actions of GIP on glucose tolerance(FIGS. 34A, 34B) and plasma insulin (FIGS. 34C, 34D) responses in obesediabetic ob/ob mice.

FIGS. 35A through 35D are a set of two line graphs (FIGS. 35A, 35C) andtwo bar graphs (FIGS. 35B, 35D) showing that acute administration of(Pro³)GIP impairs physiological meal-stimulated insulin release andworsens glycemic excursion in obese diabetic ob/ob mice.

FIGS. 36A and 36B are a set of two bar graphs showing that chronicadministration of (Pro³)GIP for 11 days decreases plasma glucose andinsulin concentrations of obese diabetic ob/ob mice.

FIGS. 37A through 37C are a set of three bar graphs showing that chronicadministration of (Pro³)GIP for 11 days decreases glycated HbA_(1c),pancreatic insulin content and associated islet hypertrophy of obesediabetic ob/ob mice.

FIGS. 38A through 38D are a set of two line graphs (FIGS. 38A, 38C) andtwo bar graphs (FIGS. 38B, 38D) showing that chronic administration of(Pro³)GIP for 11 days improves glucose tolerance of obese diabetic ob/obmice without change of circulating insulin.

FIG. 39 is a line graph showing that chronic administration of (Pro³)GIPfor 11 days improves insulin sensitivity in obese diabetic ob/ob mice.

FIG. 40 is a line graph showing that the beneficial effects of chronicadministration of (Pro³)GIP for 11 days in obese diabetic ob/ob mice arereversed 9 days after cessation of treatment.

FIGS. 41A and 41B are a set of two line graphs showing that chronicadministration of (Pro³)GIP for 11 days causes glucose intolerance innormal mice with reversal by 9 days after cessation of treatment.

FIGS. 42A through 42D are a set of two line graphs (FIGS. 42A, 42C) andtwo bar graphs (FIGS. 42B, 42D) showing the effects of (Pro³)GIP onplasma glucose and insulin response to native GIP 4 hours afteradministration.

FIGS. 43A through 43D are a set of two line graphs and two bar graphsshowing the effects of daily (Pro³)GIP administration on food intake(FIG. 43A), body weight (FIG. 43B), plasma glucose (FIG. 43C) andinsulin (FIG. 43D) concentrations in ob/ob mice.

FIGS. 44A through 44D are a set of four line graphs with inset bargraphs showing the effects of daily (Pro³)GIP administration on glucosetolerance and plasma insulin response to glucose in ob/ob mice.

FIGS. 45A through 45D are a set of two line graphs (FIGS. 45A, 45C) andtwo bar graphs (FIGS. 45B, 45D) showing the effects of daily (Pro³)GIPadministration (A; black bars) or saline (o; white bars) on glucose(FIGS. 45A, 45B) and insulin (FIGS. 45C, 45D) responses to feeding inob/ob mice fasted for 18 hours.

FIGS. 46A through 46D are a set of two line-graphs (FIGS. 46A, 46C) andtwo bar graphs (FIGS. 46B, 46D) showing the effects of daily (Pro³)GIPadministration on insulin sensitivity in ob/ob mice.

FIGS. 47A through 47D are a set of four bar graphs showing the effectsof daily (Pro³)GIP administration on pancreatic weight (FIG. 47A),insulin content (FIG. 47B), islet number (FIG. 47C) and islet diameter(FIG. 47D) in ob/ob mice.

FIGS. 48A through 48F are a set of two bar graphs (FIGS. 48A, 48D) andfour photomicrographs (FIGS. 48B, 48C, 48E, 48F), showing the effects ofdaily (Pro³)GIP administration on islet size and morphology in ob/ob)mice.

FIG. 49 is an illustration of how the GIP receptor (“GIP-R”) antagonist,(Pro³)GIP, counters beta cell hyperplasia, hyperinsulinemia and insulinresistance lead to improved glucose intolerance and diabetes control.

FIGS. 50A and 50B are a line graph and a bar graph, respectively,showing intracellular cyclic AMP production (FIG. 50A) by GIP (▴) andfatty acid derivatised GOP analogues N-AcGIP(LysPAL¹⁶) (□) andN-AcGOP(LysPAL³⁷) (●), and insulin-releasing activity of glucose (5.6mmo/l glucose; white bars), GIP (lined bars) and fatty acid derivatisedGIP analogues (FIG. 50B) N-AcGIP(LysPAL¹⁶) (grey bars) andN-AcGIP(LysPAL³⁷) (black bars) in the clonal pancreatic beta cell line,BRIN-BD11.

FIGS. 51A through 51D are a set of two line graphs (FIGS. 51A, 51C) andtwo bar graphs (FIGS. 51B, 51D) showing glucose lowering effects (FIGS.51A, 51B) and insulin-releasing activity (FIGS. 51C, 51D) of GIP andfatty acid derivatised GIP analogues in 18 hour-fasted ob/ob mice.

FIGS. 52A and 52B are a pair of bar graphs showing dose-dependenteffects of GIP and N-AcGIP(LysPAL³⁷) in ob/ob mice fasted for 18 hours.

FIGS. 53A through 53E are a set of graphs showing the effects of dailyN-AcGIP(LysPAL³⁷) (●; black bars) administration on food intake (FIG.53A), body weight (FIG. 53B), plasma glucose (FIG. 53C), insulin (FIG.53D) and glycated hemoglobin N-AcGIP(LysPAL³⁷) (12.5 nmoles/kg/day)(FIG. 53E).

FIGS. 54A through 54D are a set of two line graphs (FIGS. 54A, 54C) andtwo bar graphs (FIGS. 54B, 54D) showing the effects of dailyN-AcGIP(LysPAL³⁷) administration on glucose tolerance (FIGS. 54A, 54B)and plasma insulin response (FIGS. 54C, 54D) to glucose.

FIGS. 55A through 55D are a line graph and three bar graphs showing theeffects of daily N-AcGIP(LysPAL³⁷) administration on insulin sensitivity(FIGS. 55A, 55B) and pancreatic weight (FIG. 55C) and insulincontent-(FIG. 55D).

FIGS. 56A through 56D are a set of two line graphs (FIGS. 56A, 56C) andtwo bar graphs (FIGS. 56B, 56D) showing the retention of glucoselowering (FIGS. 56A, 56B) and insulin releasing (FIGS. 56C, 56D)activity of N-AcGIP(LysPAL³⁷) and native GOP after daily injection for14 days.

FIGS. 57A through 57D are a set of two line graphs (FIGS. 57A, 57C) andtwo bar graphs (FIGS. 57B, 57D) showing the acute glucose lowering(FIGS. 57A, 57B) and insulin releasing (FIGS. 57C, 57D) effects ofN-AcGIP(LysPAL³⁷) after 14 daily injections of either N-AcGIP(LysPAL³⁷)(12.5 nmoles/kg/day; ●; black bars), native GIP (12.5 nmoles/kg/day; ▴;lined bars) or saline vehicle (control; □; white bars).

DETAILED DESCRIPTION

The peptide analogues disclosed herein display resistance to degradationby the enzyme DPP IV. These analogues include those with alterations atresidues 1, 2 and/or 3 of the native GIP(1-42) peptide, where thealterations interfere with or delay cleavage by DPP IV. The alterationscan include chemical modification of one or more of the first threeamino acids, such as by acylation, acetylation, alkylation, glycation,conversion of a bond between two amino acids, such as to a psi-[CH₂NH]bond, or to a stable isotere bond, or addition of an isopropyl group.The alterations can also include amino acid substitutions at the 1, 2,and/or 3 position, to either a different naturally-occurring amino acid,or an amino acid not encoded by the genetic code. Other alterations arealso possible, and the object is to prevent cleavage of the peptide byDPP IV, yet still allow for insulin secretion. This may be accomplishedby alterations at other regions of the peptide, such as by alterationsthat alter the three-dimensional structure to prevent DPP IV cleavage,yet still allow insulin secretion.

Preferred alterations include chemical modifications of residues 1, 2,and 3, amino acid substitutions at residues 1, 2, and 3, and chemicalmodifications of lysine residues throughout the protein.

Particularly preferred alterations include acetylation of Tyr¹ andlinkage of a C-16 palmitate group to the epsilon amino group of a lysineresidue (especially Lys¹⁶ or Lys³⁷), or substitution of Glu³, especiallyby proline. The modification can also be the linking of, e.g., a C-8, aC-10, a C-12, a C-14, a C-18 or a C-20 palmitate group to the epsilonamino group of a lysine residue.

It has been found that longer-term, as opposed to acute, GIP receptorantagonism using Glu³-substituted forms of GIP, such as (Pro³)GIP,improve obesity-related insulin resistance and associated glucoseintolerance. This has uncovered an unexpected approach to the therapy ofobesity, insulin resistance and type 2 diabetes.

As described in Example 1 below, an N-terminally modified version of theGIP protein was prepared, as were analogues of the modified protein. Theprotein and its analogues were then evaluated in Example 2 for theirantihyperglycemic and insulin-releasing properties in vivo, and werefound to exhibit a substantial resistance to amino peptidase degradationand increased glucose lowering activity relative to native GIP.

The 42 amino acid GIP is an important incretin hormone released into thecirculation from endocrine K-cells of the duodenum and jejunum followingingestion of food. The high degree of structural conservation of GIPamong species supports the view that this peptide plays an importantrole in metabolism. Secretion of GIP is stimulated directly by activelytransported nutrients in the gut lumen without a notable input fromautonomic nerves. The most important stimulants of GIP release aresimple sugars and unsaturated long chain fatty acids, with amino acidsexerting weaker effects. As with tGLP-1, the insulin-releasing effect ofGIP is strictly glucose-dependent. This affords protection againsthypoglycemia and thereby fulfills one of the most desirable features ofany current or potentially new antidiabetic drug.

The present results demonstrate for the first time that Tyr¹-glucitolGIP displays profound resistance to serum and DPP IV degradation. UsingESI-MS the present study showed that native GIP was rapidly cleaved invitro to a major 4748.4 Da degradation product corresponding toGIP(3-42), which confirmed previous findings using matrix-assisted laserdesorption ionization time-of-flight mass spectrometry. Serumdegradation was completely inhibited by diprotin A (Ile-Pro-Ile), aspecific competitive inhibitor of DPP IV, confirming this as the mainenzyme for GIP inactivation in vivo. In contrast, Tyr¹-glucitol GIPremained almost completely intact after incubation with serum or DPP IVfor up to 12 hours. This indicates that glycation of GIP at theamino-terminal Tyr¹ residue masks the potential cleavage site from DPPIV and prevents removal of the Tyr¹-Ala² dipeptide from the N-terminuspreventing the formation of GIP(3-42).

Consistent with in vitro protection against DPP IV, administration ofTyr¹-glucitol GIP significantly enhanced the antihyperglycemic activityand insulin-releasing action of the peptide when administered withglucose to rats. Native GIP enhanced insulin release and reduced theglycemic excursion as observed in many previous studies. However,amino-terminal glycation of GIP increased the insulin-releasing andantihyperglycemic actions of the peptide by 62% and 38% respectively, asestimated from insulin area under the curve (AUC) measurements. Detailedkinetic analysis is difficult due to necessary limitation of samplingtimes, but the greater insulin concentrations following Tyr¹-glucitolGIP as opposed to GIP at 30 minutes post-injection is indicative of alonger half-life. The glycemic rise was modest in both peptide-treatedgroups and glucose concentrations following injection of Tyr¹-glucitolGIP were consistently lower than after GIP. Since the insulinotropicactions of GIP are glucose-dependent, it is likely that the relativeinsulin-releasing potency of Tyr¹-glucitol GIP is greatly underestimatedin the present in vivo experiments.

In vitro studies in the laboratory of the present inventors usingglucose-responsive clonal B-cells showed that the insulin-releasingpotency of Tyr¹ glucitol GIP was several orders of magnitude greaterthan GIP and that its effectiveness was more sensitive to change ofglucose concentrations within the physiological range. Together with thepresent in vivo observations, this suggests that N-terminal glycation ofGIP confers resistance to DPP IV degradation whilst enhancing receptorbinding and insulin secretory effects on the B-cell. These attributes ofTyr¹⁻glucitol GIP are fully expressed in vivo where DPP IV resistanceimpedes degradation of the peptide to GIP(3-42), thereby prolonging thehalf-life and enhancing effective concentrations of the intactbiologically active peptide. It is thus possible that glycated GIP isenhancing insulin secretion in vivo both by enhanced potency at thereceptor as well as improving DPP IV resistance. Thus numerous studieshave shown that GIP (3-42) and other N-terminally modified fragments,including GIP(4-42), and GIP(1742) are either weakly effective orinactive in stimulating insulin release. Furthermore, evidence existsthat N-terminal deletions of GIP result in receptor antagonistproperties in GIP receptor transfected Chinese hamster kidney cells [9],suggesting that inhibition of GIP catabolism would also reduce thepossible feedback antagonism at the receptor level by the truncatedGIP(342).

In addition to its insulinotopic actions, a number of other potentiallyimportant extrapancreatic actions of GIP may contribute to the enhancedantihyperglycemic activity and other beneficial metabolic effects ofTyr¹-glucitol GIP. These include the stimulation of glucose uptake inadipocytes, increased synthesis of fatty acids and activation oflipoprotein lipase in adipose tissue. GIP also promotes plasmatriglyceride clearance in response to oral fat loading. In liver, GIPhas been shown to enhance insulin-dependent inhibition ofglycogenolysis. GIP also reduces both glucagon-stimulated lipolysis inadipose tissue as well as hepatic glucose production. Finally, recentfindings indicate that GIP has a potent effect on glucose uptake andmetabolism in mouse isolated diaphragm muscle. This latter action may beshared with tGLP-1 and both peptides have additional benefits ofstimulating somatostatin secretion and slowing down gastric emptying andnutrient absorption.

This study demonstrates that the glycation of GIP at the aminoterminalTyr¹ residue limits GIP catabolism through impairment of the proteolyticactions of serum peptidases and thus prolongs its half-life in vivo.This effect is accompanied by enhanced antihyperglycemic activity andraised insulin concentrations in vivo, suggesting that such DPP IVresistant analogues are potentially useful therapeutic agents for NIDDM.Tyr¹-glucitol GIP appears to be particularly interesting in this regardsince such amino-terminal modification of GIP enhances rather thanimpairs glucose-dependent insulinotropic potency as was observedrecently for tGLP-1.

As shown in Table 1 in Example 3, glycated GIP, acetylated GIP,GIP(Ser²) are GIP(Abu²) more resistant than native GIP to in vitrodegradation with DPP IV. From these data GIP(Sar²) appears to be lessresistant. As shown in Table 2, all analogues tested exhibitedresistance to plasma degradation, including GIP(Sar²) which from DPP IVdata appeared least resistant of the peptides tested. DPA substantiallyinhibited degradation of GIP and all analogues tested with completeabolition of degradation in the cases of GIP(Abu²), GIP(Ser²) andglycated GIP. This indicates that DPP IV is a key factor in the in vivodegradation of GIP.

As shown in FIGS. 17-30, the glycated GIP analogue exhibited aconsiderably greater insulinotropic response relative to native GIP.N-terminal acetylated GIP exhibited a similar pattern and the GIP(Ser²)analogue also evoked a strong response. From these tests, GIP(Gly²) andGIP(Pro³) appeared to the least potent analogues in terms of insulinrelease. Other stable analogues tested, namely GIP(Abu²) and GIP(Sar²),exhibited a complex pattern of responsiveness dependent on glucoseconcentration and dose employed. Thus, very low concentrations wereextremely potent under hyperglycemic conditions (16.7 mM glucose). Thissuggests that even these analogues may prove therapeutically useful inthe treatment of type 2 diabetes where insulinotropic capacity combinedwith in vivo degradation dictates peptide potency.

A major limitation to the possible therapeutic use of both GIP and GLP-1as insulin-releasing agents for the treatment of diabetes is their rapiddegradation in vivo by dipeptidylpeptidase-IV (DPP-IV; EC 3.4.14.5).This enzyme rapidly removes the amino-terminal dipeptide from the twopeptides producing GIP(3-42) and GLP-1(9-36), which lack biologicalactivity (Gault, V. A. et al., 2002, Biochem. Biophys. Res. Commun.290:1420-1426). In searching for stable amino-terminally modified formsof GIP and GLP-1, it was discovered that a novel synthetic GIP analoguewith a single proline substitution at position 3 close to the cleavagesite, (Pro³)GIP, functioned as a potent GIP receptor antagonist.

As shown in Example 4, below, (Pro³)GIP, other Glu³-substituted forms ofGIP and GIP(3-42) are potent GIP receptor antagonists both in vitro andin vivo. Experiments evaluating the effects of chronic GIP receptorantagonism in normal mice using (Pro³)GIP demonstrated a substantial butreversible deterioration of glucose tolerance. This is entirelyconsistent with the widely recognised physiological role of GIP as animportant insulin-releasing intestinal hormone involved in theregulation of glucose disposal following feeding (Meier, J. J. et al.,2002, Regul. Pept. 107:1-13).

Most notably, and in complete contrast to normal mice, the experimentsdisclosed herein show that chronic (Pro³)GIP administration to obesediabetic ob/ob mice for 11 days does not worsen glucose intolerance anddiabetes status at all. Surprisingly, GIP receptor antagonism in thisobese insulin resistant model was associated with highly substantialimprovements of glycated HbA_(1c), plasma glucose and insulinconcentrations, glucose tolerance and insulin sensitivity. Pancreaticinsulin content was also decreased and the characteristic islethypertrophy of the obese mutant was partially reversed. These latterobservations indicate a decreased secretory demand for endogenousinsulin following (Pro³)GIP as a result of improved insulin resistance.

Indeed, insulin sensitivity tests conducted in ob/ob mice 11 days into(Pro³)GIP treatment revealed a substantial improvement in tissue insulininsensitivity, which more than compensated for the functional ablationof the insulin-releasing GIP component of the enteroinsular axis. Theexact mechanism responsible for this effect on insulin sensitivity isunknown but ablation of direct action of circulating GIP on adiposetissue metabolism is a likely candidate. Also noteworthy was the factthat all these beneficial actions of (Pro³)GIP in obese diabetic ob/obmice were reversed within 9 days cessation of treatment.

These results clearly indicate that (Pro³)GIP and other analogues basedon Glu³-substituted or N-terminally truncated forms of thegastrointestinal hormone GIP can offer an important therapeutic means ofalleviating insulin resistance for the treatment of obesity, theso-called insulin resistant (metabolic) syndrome and type 2 diabetes inhumans.

Some studies have attempted to enhance incretin action using DPP IVinhibitors or stable analogs of GLP-1 and GIP for the treatment of type2 diabetes (Green, B. D. et al., 2004, Curr. Pharm. Des. 10: In Press;Drucker, D. J. et al., Diabetes Care 10:2929-2940). Such an approach isreliant on the possibility that incretin action is defective in diabetesand that the underlying defects responsible for metabolic disarray mightbe over-ridden by exogenous GLP-1 or GIP administration. There is someevidence for a beneficial and possibly therapeutic role of both GLP-1and GIP analogs in diabetes (Meier, J. J. et al., 2002, Regul. Pept.107:1-13; Gault, V. A. et al., 2003, Biochem Biophys Res Commun308:207-213; Holst, J. J. et al., 2004, Am. J. Physiol. Endocrinol.Metab. 287:E199-E206; Green, B. D. et al., 2004, Curr. Pharm. Des. 10:In Press; Drucker, D. J. et al., Diabetes Care 10:2929-2940).Nevertheless, understanding of the possible involvement of incretinhormones in the pathophysiology of diabetes is lacking, partly due tocross-reaction of classical GLP-1 and GIP radioimmunoassays with thepredominant DPP IV-generated truncated peptide forms, GLP-1(9-36) andGIP(3-42), which circulate at particularly high concentrations (Meier,J. J. et al., 2002, Regul. Pept. 107:1-13). Some clinical studies seemsto suggest existence of a defect in the secretion of GLP-1 and a defectin the action of GIP in type 2 diabetes (Holst, J. J. et al., 2004, Am.J. Physiol. Endocrinol. Metab. 287:E199-E206). However, the basis forsuch a conclusion is not impressive given the many previouscontradictory human studies (Morgan, L. M., “Insulin secretion and theenteroinsular axis,” In: Nutrient regulation of insulin secretion,Flatt, P. R., ed., London, Portland Press, 1992, p. 1-22), and thelikelihood that the reported insensitivity of pancreatic beta cells toGIP (Vilsboll, T. et al., 2002, Diabetologia 45:1111-1119) may reflect ageneralized secretory dysfunction rather than a specific cellular defect(Meier, J. J. et al., 2003, Metabolism 52:1579-1585). Indeed, theinsulin secretory response to all secretagogues, including GLP-1 iscompromised in type 2 diabetes (Kjems, L. L. et al., 2003, Diabetes52:380-386; Flatt, P. R. et al., “Defective insulin secretion indiabetes and insulinoma,” in Nutrient regulation of insulin secretion,Flatt P. R., ed. London, Portland Press, 1992, p. 341-386). Thus theproposed use of GLP-1 and GIP for diabetes therapy is reliant on peptideengineering to provide analogs of incretin hormones with improvedpotency due to DPP IV resistance, decreased renal clearance and/orenhanced GIP receptor and post-receptor activity (Gault, V. A. et al.,2003, Biochem Biophys Res Commun 308:207-213).

Although no single animal model can match the complex etiology of type 2diabetes in man, studies of the ob/ob syndrome in mice have highlightednotable abnormalities of GIP in relation to the interplay betweenhyperphagia, hyperinsulinemia and the metabolic demise associated withprogressive obesity-diabetes (Flatt, P. R. et al., 1983, Diabetes32:433-435; Flatt, P. R. et al., 1984, J. Endocrinol. 101:249-256;Bailey, C. J. et al., 1986, Acta Endocrinol. (Copenh) 112:224-229).These animals constitute a model of non-insulin dependent diabetesassociated with gross obesity and severe insulin resistance, driven byleptin deficiency (Bailey, C. J. et al., “Animal syndromes resemblingtype 2 diabetes,” in Textbook of Diabetes, 3rd ed. Pickup J. C. &Williams G., eds. Oxford, Blackwell Science Ltd., 2003, p. 25.1-25.30).Furthermore, recent research suggests an interaction between leptin andthe enteroinsular axis (Anini, Y. et al., 2003, Diabetes 52:252-259) andthat over-stimulation of the GIP receptor (“GIP-R”) on adipocytesappears to be an important contributor to fat deposition in ob/ob mice(Miyawaki, K. et al., 2002, Nat. Med. 8:738-742).

As shown in Example 5, below, daily injections of the stable andspecific GIP-R antagonist, (Pro³)GIP can be used to chemically ablatethe GIP-R and evaluate the role of endogenous circulating GIP inobesity-diabetes as manifested in ob/ob mice. The results reveal acardinal role for GIP in insulin resistance and associated metabolicdisturbances, and provide the first experimental evidence that GIP-Rantagonists might provide a novel and effective means of treatingobesity-driven forms of type 2 diabetes.

Knock-out of the GIP-R in normal mice has been shown to result insignificant impairment of glucose tolerance and meal-induced insulinsecretion without appreciable effects on food intake, body weight orbasal glucose or insulin concentrations (Miyawaki, K. et al., 1999,Proc. Nat. Acad. Sci. USA 96:14843-14847). More recent studies withgenetic GIP-R knockout mice have corroborated these findings andadditionally shown that GIP has a significant involvement in theenteroinsular axis (Pederson, R. A. et al., 1998, Diabetes 47:1046-1052;Pamir, N. et al., 2003, Am. J. Physiol. Endocrinol. Metab.284:E931-939). However, double knockout of receptors for GLP-1 and GIPresults in a surprisingly modest deterioration of glucose homeostasis(Hansotia, T., et al., 2004, Diabetes 53:1326-1335; Preitner, F., etal., 2004, J. Clin. Invest. 113:635-645), indicating possibleup-regulation of compensatory mechanisms during life-long deletion ofGLP-1 and GIP receptors.

The analogue (Pro³)GIP can be used as a specific and potent antagonistof the GIP-R that is highly stable and resistant to DPP IV-mediateddegradation (Gault, V. A. et al., 2002, Biochem. Biophys. Res. Commun.290:1420-1426). Using (Pro³)GIP acutely, the results disclosd hereinhighlight the involvement of GIP in the plasma insulin response tofeeding and the enteroinsular axis of ob/ob mice (Gault, V. A. et al.,2003, Diabetologia 46:222-230). Comparison with the effects of theGLP-1-R antagonist, exendin(9-39), indicates that GIP contributessubstantially to the insulin releasing actions of the enteroinsular axisand represents the major physiological incretin (Gault, V. A. et al.,2003, Diabetologia 46:222-230). Once daily administration of (Pro³)GIPto normal mice for 11 days results in the reversible impairment ofglucose tolerance associated with decreased insulin sensitivity (Irwin,N., 2004, Biol. Chem. 385-845-852). Basal and postprandial insulinsecretion together with pancreatic insulin content and islet morphologywere unchanged. Thus longer-term chemical ablation of GIP-R functionwith daily (Pro³)GIP can mimic the phenotype induced by genetic GIP-Rknockout in mice with the exception of revealing a potentially importantadditional effect of endogenous GIP on insulin action, which appears tobe independent of enhanced insulin secretion.

Far from reproducing this predicted scenario and the metabolicdeterioration observed following genetic or chemical knockout of theGIP-R in normal mice (Miyawaki, K. et al., 1999, Proc. Nat. Acad. Sci.USA 96:14843-14847; Irwin, N., 2004, Biol. Chem. 385:845-852), ob/obmice treated with daily (Pro³)GIP for 11 days exhibited a markedimprovement in diabetic status. This included decreased fasting andbasal hyperglycemia, lowered glycated hemoglobin, improved glucosetolerance and a significantly diminished glycemic excursion followingfeeding. Notably, basal and glucose-stimulated plasma insulinconcentrations were decreased, suggesting that insulin sensitivity musthave improved significantly following (Pro³)GIP in order to restrain thehyperglycemia. Indeed, insulin sensitivity tests conducted after 11 daysof (Pro³)GIP administration revealed a 57% increase in theglucose-lowering action of exogenous insulin. Bearing in mind that theseverity of the ob/ob syndrome represents a tough test for currentantidiabetic drugs, including insulin, sulfonylureas, metformin andthiazolidenediones (Flatt, P. R. et al., “Defective insulin secretion indiabetes and insulinoma,” in Nutrient regulation of insulin secretion,Flatt P. R., ed. London, Portland Press, 1992, p. 341-386; Stevenson, R.W. et al., 1995, The Diabetes Annual 9:175-191; Wiermsperger, N. F.,“Preclinical pharmacology of biguanides,” Handbook of ExperimentalPharmacology 119:305-358, 1996), induction of such rapid and reversiblechanges by GIP-R blockade using (Pro³)GIP is unprecedented.

It is important to note that the above effects were observedindependently of any change in food intake or body weight in (Pro³)GIPtreated ob/ob mice. This accords with the view that endogenous GIP lackseffects on feeding activity (Meier, J. J. et al., 2002, Regul. Pept.107:1-13). However, the observation on body weight contrasts withfindings in ob/ob mice cross-bred to genetically knockout GIP-R function(Miyawaki, K. et al., 2002, Nat. Med. 8:738-742). Thus in thesetransgenic mice, life-long depletion of GIP-R function was associatedwith decreased body weight gain and significant amelioration of bothadiposity and insulin resistance compared with control(Lep^(ob)/Lep^(ob)) mice (Miyawaki, K. et al., 2002, Nat. Med.8:738-742). In this previous study, the improvement of insulinsensitivity may have been a simple consequence of reduced adipose tissuemass as this would significantly enhance peripheral glucose disposal(Bailey, C. J. et al., “Animal syndromes resembling type 2 diabetes,” inTextbook of Diabetes, 3rd ed. Pickup J. C. & Williams G., eds. Oxford,Blackwell Science Ltd., 2003, p. 25.1-25.30). However, the presentresults observed in rapid time and without effects on feeding or bodyweight clearly indicate the involvement of an alternative mechanism.

The most plausible explanation for the present data stem fromappreciation of the key milestones in the age-dependent progression ofthe ob/ob syndrome on the Aston background as depicted in FIG. 49, whichis an illustration of how the GIP-R antagonist, (Pro³)GIP, counters betacell hyperplasia, hyperinsulinemia and insulin resistance lead toimproved glucose intolerance and diabetes control. Possible longer-termdirect actions of GIP on adipocyte function and fat stores, suggested bystudies in GIP-R knockout ob/ob mice have been omitted.

Due to double recessive ob mutation and resulting leptin deficiency,young ob/ob mice develop a profound early hyperphagia (Bailey, C. J., etal., 1982, Int. J. Obes. 6:11-21). Substantial enteroendocrinestimulation results in K-cell hyperplasia and markedly elevatedconcentrations of intestinal and circulating GIP (Flatt, P. R. et al.,1983, Diabetes 32:433-435; Flatt, P. R. et al., 1984, J. Endocrinol.101:249-256; Bailey, C. J. et al., 1986, Acta Endocrinol. (Copenh)112:224-229). This in turn promotes islet hypertrophy and beta cellhyperplasia (Bailey, C. J., et al., 1982, Int. J. Obes. 6:11-21)together with marked hyperinsulinemia and mounting insulin resistance(Flatt, P. R., et al., 1981, Horm Metab Res 13:556-560). This processmanifests itself in terms of rising basal hyperglycemia and glucoseintolerance. A vicious spiral is thus established wherein beta cellcompensation results in marked hyperinsulinemia which attempts tomoderate increasing insulin resistance (Bailey, C. J., et al., 1982,Int. J. Obes. 6:11-21; Flatt, P. R., et al., 1981, Horm Metab Res13:556-560). Viewed in this context, it is clear that chemical ablationof GIP-R function with daily (Pro³)GIP will decrease beta cellstimulation and hyperinsulinemia. However, instead of causing furtherimpairment of glucose homeostasis, a preferentially marked improvementof insulin sensitivity results in a substantial improvement of themetabolic syndrome. Further support for this scenario, is the partialamelioration of islet hypertrophy and beta cell hyperplasia in (Pro³)GIPtreated ob/ob mice (FIG. 48). Notably, average islet diameter wasdiminished with the largest islets (>15 mm) being replaced by a greaterproportion with small or medium diameters (0.1-15 mm). These effectswere largely reversed by 9 day cessation of treatment, supporting theidea of active islet and beta cell growth in adult ob/ob mice (Bailey,C. J., et al., 1982, Int. J. Obes. 6:1 i-21). Recent observationsindicate that GIP acts as a mitotic stimulus and anti-apoptotic agent tothe beta cell (Pospisilik, J. A. et al., 2003, Diabetes 52:741-750;Trumper, A. et al., 2001, Mol. Endocrinol. 15:1559-1570; Ehses, J. A. etal., 2003, Endocrinology 144:4433-4445, Trumper, A. et al., 2002, J.Endocrinol. 174:233-246). Thus, it is believed that negative effects of(Pro³)GIP on islet size reflects a combination of decreasedproliferation and increased apoptosis of beta cells.

The results shown in Example 5 have demonstrated for the first time thatdaily administration of the GIP-R antagonist, (Pro³)GIP, improvesglucose tolerance and ameliorates insulin resistance and abnormalitiesof islet structure and function in ob/ob mice. Notably, these effectswere reversed by discontinuation of (Pro³)GIP for 9 days. Freedom fromany obvious side effects also accords with earlier observations innormal mice (Irwin, N., 2004, Biol. Chem. 385:845-852) and micegenetically engineered with life-long GIP-R deficiency (Miyawaki, K. etal., 2002, Nat. Med. 8:738-742). The present observations point to acardinal role of endogenous GIP in the pathogenesis of obese-insulinresistant-diabetes. More importantly, the data indicate that GIP-Rantagonists, such as (Pro 3)GIP, provide a novel, physiological andeffective means to treat obese type 2 diabetes through the alleviationof insulin resistance.

In Example 6, fatty acid derivatisation was used to develop two novellong-acting, N-terminally modified GIP analogues (N-AcGIP(LysPAL¹⁶) andN-AcGIP(LysPAL³⁷)).

Degradation studies were carried out with dipeptidylpeptidase IV (DPPIV). Cyclic AMP production was assessed using GIP receptor transfectedCHL fibroblasts. In vitro insulin release was assessed in BRIN-BD11cells. Insulinotropic and glycaemic responses to acute and long-termpeptide administration were evaluated in obese diabetic (ob/ob) mice.

In contrast to GIP both analogues displayed resistance to DPP IVdegradation. The analogues also stimulated cyclic AMP production andexhibited significantly improved in vitro insulin secretion compared tocontrol. Administration of N-AcGIP(LysPAL¹⁶) or N-AcGIP(LysPAL³⁷)together with glucose in ob/ob mice significantly reduced the glycaemicexcursion and improved the insulinotropic response compared to GIP.Dose-response studies with N-AcGIP(LysPAL³⁷) revealed highly significantdecreases in the overall glycaemic excursion and increases incirculating insulin even with 6.25 nmoles/kg. Once daily injection ofob/ob mice with N-AcGIP(LysPAL³⁷) over 14 days significantly decreasedplasma glucose, glycated haemoglobin and improved glucose tolerancecompared with saline or native GIP. Plasma and pancreatic insulin weresignificantly increased, together with a significant enhancement in theinsulin response to glucose and a notable improvement of insulinsensitivity. No evidence was found for GIP-receptor desensitization andthe metabolic effects of N-AcGIP(LysPAL³⁷) were independent of anychange in feeding or body weight.

These results show that novel fatty acid derivatised, N-terminallymodified analogues of GIP such as N-AcGIP(LysPAL³⁷), may havesignificant potential for the treatment of type 2 diabetes.

One approach to counter both renal clearance and enzyme degradation ofGIP concerns the utilisation of fatty acid derivatisation together withN-terminal modification. Fatty acid derivatisation has previously beenshown to prolong the half-life of insulin (Kurtzhals, P. et al., 1995,Biochem. J. 312: 725-731) and the sister incretin glucagon-likepeptide-1 (GLP-1) (Knudsen, L. B. et al., 2000, J. Med. Chem. 43:1664-1669; Green, B. D. et al., 2004, Biol. Chem. 385: 169-177; Kim, J.G. et al., 2003, Diabetes 52: 751-759). A number of N-terminallymodified GIP analogues have been developed which exhibit profoundresistance to DPP IV (Hinke, S. A. et al., 2002, Diabetes 51: 656-661;Gault, V. A. et al., 2002, Biochem. J. 367: 913-920; Gault, V. A. etal., 2003, J. Endocrinol. 176: 133-141; O'Harte, F. P. M. et al., 1999,Diabetes 48: 758-765). Several of these, most notably those modified atTyr¹ of GIP with an addition of an acetyl, glucitol, pyroglutamyl orFmoc adduct, exhibit enhanced activity at the GIP receptor in vitro(Gault, V. A. et al., 2002, Biochem. J. 367: 913-920; O'Harte, F. P. M.et al., 1999, Diabetes 48: 758-765; O'Harte, F. P. M. et al., 2002,Diabetologia 45: 1281-1291). As a result of degradation resistance andenhanced cellular activity, these analogues display enhanced andprotracted antihyperglycaemic and insulin-releasing activity whenadministered acutely to animals with obesity-diabetes (Hinke, S. A. etal., 2002, Diabetes 51: 656-661; Gault, V. A. et al., 2002, Biochem. J.367: 913-920; Gault, V. A. et al., 2003, J. Endocrinol. 176: 133-141;O'Harte, F. P. M. et al., 1999, Diabetes 48: 758-765; O'Harte, F. P. M.et al., 2002, Diabetologia 45: 1281-1291). Of these, N-AcGIP has emergedas the most effective DPP IV-resistant analogue, substantiallyaugmenting the plasma insulin response and curtailing the glycaemicexcursion following conjoint administration with glucose to ob/ob mice(O'Harte, F. P. M. et al., 2002, Diabetologia 45: 1281-1291).

Example 6 was designed to evaluate the metabolic stability, biologicalactivity and antidiabetic potential of novel second generation fattyacid derivatised, N-terminally modified N-AcGIP analogues,N-AcGIP(LysPAL¹⁶) and N-AcGIP(LysPAL³⁷). Both GIP analogues contain aC-16 palmitate group linked to the epsilon-amino group of Lys atpositions 16 or 37, in combination with an N-terminal (Tyr¹) acetylgroup (O'Harte, F. P. M. et al., 2002, Diabetologia 45: 1281-1291). Therelative stability to DPP IV degradation, insulin secretion and cyclicAMP properties were examined in vitro together with acute anddose-response studies in obese diabetic ob/ob mice. The most effectiveanalogue, N-AcGIP(LysPAL³⁷) was administered to ob/ob mice by once dailyintraperitoneal injection for 14 days prior to evaluation of glucosehomeostasis, pancreatic beta cell function and insulin sensitivity.Possible desensitization of GIP receptor action by prolonged exposure toelevated concentrations of N-AcGIP(LysPAL³⁷) was also examined. Theresults indicate the particular promise of the novel second generationN-terminally acetylated GIP analogue, N-AcGIP(LysPAL³⁷), as a potentialtherapeutic agent for the treatment of type 2 diabetes.

Despite their many attributes, DPP IV-resistant analogues of GIP andGLP-1, like their native counterparts, are still subject to renalfiltration. To circumvent this problem, fatty acid derivatisation hasbeen used to improve the duration of action of GLP-1 (Knudsen, L. B. etal., 2000, J. Med. Chem. 43: 1664-1669; Green, B. D. et al., 2004, Biol.Chem. 385: 169-177; Kim, J. G. et al., 2003, Diabetes 52: 751-759). Themost promising analogue, NN2211 (Liraglutide), appears effective inimproving blood glucose control in type 2 diabetic subjects despite atendency towards promotion of nausea possibly due to slowing of gastricemptying (Agersø, H. et al., 2002, Diabetologia 45: 195-202).

Example 6 describes the results of introducing two specificmodifications to the native GIP hormone, namely N-terminal acetylationand C-terminal fatty acid derivatisation. N-terminal acetylation wasemployed, as previously described (O'Harte, F. P. M. et al., 2002,Diabetologia 45: 1281-1291), to significantly enhance stability to DPPIV. In contrast, conjugation of a C-16 palmitate residue at theepsilon-amino group of Lys¹⁶ or Lys³⁷ was introduced to extend thebiological half-life through binding to circulating proteins (Kurtzhals,P. et al., 1995, Biochem. J. 312: 725-731). Unlike the native peptide,both GOP analogues appeared to be completely resistant to enzymaticbreakdown by DPP IV, which corroborates previous observations withN-AcGIP (O'Harte, F. P. M. et al., 2002, Diabetologia 45: 1281-1291).Furthermore, both analogues displayed similar or slightly betterinsulin-releasing and cyclic AMP generating properties to native GIP andN-AcGIP when tested in the in vitro cellular systems (O'Harte, F. P. M.et al., 2002, Diabetologia 45: 1281-1291).

To assess the antihyperglycaemic and insulinotropic potential of thefatty acid derivatised GOP analogues in vivo, obese diabetic (ob/ob)mice were employed. The ob/ob syndrome is an extensively studied modelof spontaneous obesity and diabetes, exhibiting hyperphagia, markedobesity, moderate hyperglycaemia and severe hyperinsulinemia (Bailey, C.J. et al., 1982, Int. J. Obesity 6: 11-21). As described in previousstudies (Gault, V. A. et al., 2002, Biochem. J. 367: 913-920; Gault, V.A. et al., 2003, J. Endocrinol. 176: 133-141), native GIP only modestlyreduced the glycaemic excursion in ob/ob mice reflecting the severeinsulin resistance of this mutant animal model (Bailey, C. J. et al.,1982, Int. J. Obesity 6: 11-21). In sharp contrast, both N-acetylatedGIP analogues additionally substituted with a palmitate molecule atLys¹⁶ or Lys³⁷ (N-AcGIP(LysPAL¹⁶) and N-AcGIP(LysPAL³⁷)) significantlylowered plasma glucose levels compared to the native peptide. This wasaccompanied by significantly enhanced insulin-releasing activity,especially in the case of N-AcGIP(LysPAL³⁷). The significantlyprotracted insulinotropic response to both fatty acid derivatised GIPanalogues at 60 minutes despite substantially lower plasma glucose isindicative of an extended plasma half-life. This may be due to bindingof both palmitate derivatised GOP analogues to serum albumin, thereforesignificantly impairing their clearance via the kidneys (Meier, J. J. etal., 2004, Diabetes 53: 654-662). However, further studies includingestablishment of sensitive and specific immunoassays for the novel GIPanalogues would be needed to confirm such actions.

N-AcGIP(LysPAL³⁷) appeared to be the best fatty acid derivatisedanalogue displaying a more protracted, significantly enhancedinsulin-releasing potency over N-AcGIP(LysPAL¹⁶) in vivo. Reasons forthe increased potency of N-AcGIP(LysPAL³⁷) remain unclear, but oneexplanation is an extended half-life. Another possibility may be that afatty acid chain linked to the Lys closer to the C-terminus of thepeptide may have less of a detrimental effect upon the bioactive regionof the molecule known to be located within the N-terminus (Gault, V. A.et al., 2002, Biosci. Rep. 22: 523-528; Hinke, S. A. et al., 2001,Biochim. Biophys. Acta 1547: 143-55; Manhart, S. et al., 2003,Biochemistry 42: 3081-3088). However, similarities between the in vitrobiological activities of the two palmitate substituted analogues makethis less likely.

Given that N-AcGIP(LysPAL³⁷) was the more potent of the two analogues invivo, it was further utilised in dose-response studies. Considering thatnative GIP itself has only very modest effects in ob/ob mice, assometimes observed with type 2 diabetic subjects (Nauck, M. A. et al.,1993, J. Clin. Invest. 91: 301-307; Meier, J. J. et al., 2004, Diabetes53: 220-224; Vilsboll, T. et al., 2002, Diabetologia 45: 1111-1119), itis remarkable that N-AcGIP(LysPAL³⁷), even at the lowest dose of 6.25nmoles/kg, exhibited significant glucose-lowering and insulinotropicactivity when administered with glucose. Considering N-AcGIP(LysPAL³⁷)is subject to albumin binding, the fact that it is still highlybiologically active even at lower concentrations indicates strikingpotency.

Daily administration of N-AcGIP(LysPAL³⁷) to young adult ob/ob mice byintraperitoneal injection (12.5 nmoles/kg) resulted in a progressivelowering of plasma glucose concentrations and a significant decrease ofglycated haemoglobin by 14 days. This was associated with a substantialimprovement of glucose tolerance. Importantly food intake and bodyweight were unchanged ruling out the possibility that improvement ofglucose homeostasis was merely the consequence of body weight loss.These observations also indicate that N-AcGIP(LysPAL³⁷) did not exertany untoward toxic actions affecting feeding over the study period. Thisis in harmony with recent studies showing that GIP does not inhibitgastric emptying (Meier, J. J. et al., 2003, Am. J. Physiol. Endocrinol.Metab. 286: 621-625). Daily administration of native GIP to ob/ob micefor 14 days had no effect on any of the parameters measure, consistentwith the very short half-life of the native GIP in vivo.

As expected, a key component of the beneficial action ofN-AcGIP(LysPAL³⁷) concerned effects on beta-cells. Thus although nativeGIP is a weak stimulus to insulin secretion in ob/ob mice at the agestudied, plasma and pancreatic insulin concentrations were raised inob/ob mice receiving the novel fatty acid derivatised analogue. This isconsistent with the action of GIP as a promoter of proinsulin geneexpression (Wang, Y. et al., 1996, Mol. Cell. Endocrinol. 116:81-87) andexemplifies the increased potency reported for N-terminally modified GIPanalogues in this animal model of diabetes (Hinke, S. A. et al., 2002,Diabetes 51: 656-661; Gault, V. A. et al., 2002, Biochem. J. 367:913-920; Gault, V. A. et al., 2003, J. Endocrinol. 176: 133-141;O'Harte, F. P. M. et al., 1999, Diabetes 48: 758-765; O'Harte, F. P. M.et al., 2002, Diabetologia 45: 1281-1291). Furthermore, the insulinresponse to glucose was significantly enhanced in ob/ob mice receivingN-AcGIP(LysPAL³⁷). This ability to augment or restore pancreatic betacell glucose responsiveness has been similarly observed with GLP-1(Holz, G. G. et al., 1993, Nature 28: 362-365; Flamez, D. et al., 1998,Diabetes 47: 646-652). As with observations on glycaemic control, noneof these attributes were reproduced by daily injections of native GIP.

Results of insulin sensitivity tests conducted after 14 days treatmentindicate that the improvement of diabetic status achieved in ob/ob micewith N-AcGIP(LysPAL³⁷) was not solely due to the potentiation of insulinsecretion. Thus, these animals also exhibited a significant improvementof insulin sensitivity compared to the GIP or saline treated groups.Given that hyperinsulinemia is generally believed to down-regulateinsulin receptor function (Marshall, S. et al., 1981, Diabetes 30:746-753), this suggests that N-AcGIP(LysPAL³⁷) may exert othercompensatory effects. Further study is necessary to evaluate this aspectbut possibilities include inhibition of counter-regulatory hormones andeffects on extrapancreatic sites such as muscle, adipose tissue andliver (Morgan, L. M. et al., 1996, Biochem. Soc. Trans. 24:585-591;O'Harte, F. P. M. et al., 1998, J. Endocrinol. 156: 237-243; Yip, R. G.et al., 1998, Endocrinology 139: 4004-4007).

Irrespective of knowledge of the full range of actions contributing tothe antihyperglycaemic effect of N-AcGIP(LysPAL³⁷), a currentlyenvisaged problem of long-term treatment with stable analogues of GIP orGLP-1 concerns desensitization of hormone receptor action (Delmeire, D.et al., 2004, Biochem. Pharmacol. 68: 33-39). Although this has beenobserved during prolonged exposure of pancreatic beta cells to GIP inrats (Tseng, C. C. et al., 1996, Am. J. Physiol. 270: E661-E666), therewas no evidence that treatment with N-AcGIP(LysPAL³⁷) for 14 dayscompromised the glucose lowering or insulin releasing actions ofN-AcGIP(LysPAL³⁷). Thus the antidiabetic actions of N-AcGIP(LysPAL³⁷)were clearly evident when the analogue was administered acutely togetherwith glucose. Furthermore, the acute effects of N-AcGIP(LysPAL³⁷) insuch experiments were identical in groups of ob/ob mice receiving eitherN-AcGIP(LysPAL³⁷), native GIP or saline injections for 14 days.

Such data clearly indicate that prolonged exposure to N-AcGIP(LysPAL³⁷)does not induce and possibly overcomes inherent GIP receptordesensitization in ob/ob mice. Given the high circulating concentrationsof GIP in these obese-diabetic rodents (Flatt, P. R. et al., 1983,Diabetes 32: 433-435; Flatt, P. R. et al., 1984, J. Endocrinol. 101:249-256), it is tempting to link beta cell refractoriness to GIP evidentin ob/ob mice to simple receptor desensitization at the hands ofinappropriate secretion and metabolism of GIP.

The data shown herein demonstrate that N-terminally acetylated GOPcarrying a palmitate group linked to Lys at position 37 displaysresistance to DPP IV and an impressive profile of bioactivity manifestedby potent and long-acting glucose-lowering activity in a commonlyemployed animal model of obesity-diabetes. This activity profileprovides strong encouragement for the development of long-acting fattyacid derivatised N-terminally modified analogues of GOP for theonce-daily treatment of type 2 diabetes.

The peptide analogues of the present invention have use in treatingdiseases and conditions caused by improper modulation of insulin levels,including diabetes, type 2 diabetes, insulin resistance, insulinresistant metabolic syndrome (Syndrome X), and obesity.

A peptide analogue produced by the methods of the present invention canbe used in a pharmaceutical composition, wherein the analogue iscombined with a pharmaceutically acceptable carrier. Such a compositionmay also contain (in addition to the analogue and a carrier) diluents,fillers, salts, buffers, stabilizers, solubilizers, and other materialswell known in the art. The term “pharmaceutically acceptable” means anon-toxic material that does not interfere with the effectiveness of thebiological activity of the active ingredient(s). The characteristics ofthe carrier will depend on the route of administration.

Administration of the peptide analogue of the present invention used inthe pharmaceutical composition or to practice the method of the presentinvention can be carried out in a variety of conventional ways, such asby oral ingestion, inhalation, topical application or cutaneous,subcutaneous, intraperitoneal, parenteral or intravenous injection.Administration can be internal or external; or local, topical orsystemic.

The compositions containing a peptide analogue of this invention can beadministered intravenously, as by injection of a unit dose, for example.The term “unit dose” when used in reference to a therapeutic compositionof the present invention refers to physically discrete units suitable asunitary dosage for the subject, each unit containing a predeterminedquantity of active material calculated to produce the desiredtherapeutic effect in association with the required diluent, i.e.,carrier or vehicle.

Formulations suitable for parenteral administration include aqueous andnon-aqueous sterile injection solutions which may contain anti-oxidants,buffers, bacteriostats and solutes which render the formulation isotonicwith the blood of the intended recipient; and aqueous and non-aqueoussterile suspensions which may include suspending agents and thickeningagents. The formulations may be presented in unit-dose or multi-dosecontainers, for example, sealed ampules and vials, and may be stored ina freeze-dried (lyophilized) condition requiring only the addition ofthe sterile liquid carrier, for example, water for injections,immediately prior to use. Extemporaneous injection solutions andsuspensions may be prepared from sterile powders, granules and tabletsof the kind previously described.

When a therapeutically effective amount of the composition of thepresent invention is administered orally, the composition of the presentinvention will be in the form of a tablet, capsule, powder, solution orelixir. When administered in tablet form, the pharmaceutical compositionof the invention may additionally contain a solid carrier such as agelatin or an adjuvant. The tablet, capsule, and powder contain fromabout 5 to 95% protein of the present invention, and preferably fromabout 25 to 90% protein of the present invention. When administered inliquid form, a liquid carrier such as water, petroleum, oils of animalor plant origin such as peanut oil, mineral oil, soybean oil, or sesameoil, or synthetic oils may be added. The liquid form of thepharmaceutical composition may further contain physiological salinesolution, dextrose or other saccharide solution, or glycols such asethylene glycol, propylene glycol or polyethylene glycol. Whenadministered in liquid form, the pharmaceutical composition containsfrom about 0.5 to 90% by weight of the composition of the presentinvention, and preferably from about 1 to 50% of the composition of thepresent invention.

When a therapeutically effective amount of the composition of thepresent invention is administered by intravenous, cutaneous orsubcutaneous injection, the composition of the present invention will bein the form of a pyrogen-free, parenterally acceptable aqueous solution.The preparation of such parenterally acceptable protein solutions,having due regard to pH, isotonicity, stability, and the like, is withinthe skill in the art. A preferred pharmaceutical composition forintravenous, cutaneous, or subcutaneous injection should contain, inaddition to the composition of the present invention, an isotonicvehicle such as Sodium Chloride Injection, Ringer's Injection, DextroseInjection, Dextrose and Sodium Chloride Injection, Lactated Ringer'sInjection, or other vehicle as known in the art. The pharmaceuticalcomposition of the present invention may also contain stabilizers,preservatives, buffers, antioxidants, or other additives known to thoseof skill in the art.

Use of timed release or sustained release delivery systems are alsoincluded. A sustained-release matrix, as used herein, is a matrix madeof materials, usually polymers, which are degradable by enzymatic oracid/base hydrolysis or by dissolution. Once inserted into the body, thematrix is acted upon by enzymes and body fluids. The sustained-releasematrix desirably is chosen from biocompatible materials such asliposomes, polylactides (polylactic acid), polyglycolide (polymer ofglycolic acid), polylactide co-glycolide (co-polymers of lactic acid andglycolic acid) polyanhydrides, poly(ortho)esters, polyproteins,hyaluronic acid, collagen, chondroitin sulfate, carboxylic acids, fattyacids, phospholipids, polysaccharides, nucleic acids, polyamino acids,amino acids such as phenylalanine, tyrosine, isoleucine,polynucleotides, polyvinyl propylene, polyvinylpyrrolidone and silicone.A preferred biodegradable matrix is a matrix of one of eitherpolylactide, polyglycolide, or polylactide co-glycolide (co-polymers oflactic acid and glycolic acid).

The therapeutic compositions can include pharmaceutically acceptablesalts of the components therein, e.g., which may be derived frominorganic or organic acids. By “pharmaceutically acceptable salt” ismeant those salts which are, within the scope of sound medicaljudgement, suitable for use in contact with the tissues of humans andlower animals without undue toxicity, irritation, allergic response andthe like and are commensurate with a reasonable benefit/risk ratio.Pharmaceutically acceptable salts are well-known in the art. Forexample, S. M. Berge, et al., describe pharmaceutically acceptable saltsin detail in J. Pharmaceutical Sciences (1977) 66:1 et seq., which isincorporated herein by reference in its entirety. Pharmaceuticallyacceptable salts include the acid addition salts (formed with the freeamino groups of the polypeptide) that are formed with inorganic acidssuch as, for example, hydrochloric or phosphoric acids, or such organicacids as acetic, tartaric, mandelic and the like. Salts formed with thefree carboxyl groups can also be derived from inorganic bases such as,for example, sodium, potassium, ammonium, calcium or ferric hydroxides,and such organic bases as isopropylamine, trimethylamine, 2-ethylaminoethanol, histidine, procaine and the like. The salts may be prepared insitu during the final isolation and purification of the compounds of theinvention or separately by reacting a free base function with a suitableorganic acid. Representative acid addition salts include, but are notlimited to acetate, adipate, alginate, citrate, aspartate, benzoate,benzenesulfonate, bisulfate, butyrate, camphorate, camphorsufonate,digluconate, glycerophosphate, hemisulfate, heptonoate, hexanoate,fumarate, hydrochloride, hydrobromide, hydroiodide,2-hydroxymethanesulfonate (isethionate), lactate, maleate,methanesulfonate, nicotinate, 2-naphthalenesulfonate, oxalate, pamoate,pectinate, persulfate, 3-phenylpropionate, picrate, pivalate,propionate, succinate, tartate, thiocyanate, phosphate, glutamate,bicarbonate, p-toluenesulfonate and undecanoate. Also, the basicnitrogen-containing groups can be quaternized with such agents as loweralkyl halides such as methyl, ethyl, propyl, and butyl chlorides,bromides and iodides; dialkyl sulfates like dimethyl, diethyl, dibutyl,and diamyl sulfates; long chain halides such as decyl, lauryl, myristyland stearyl chlorides, bromides and iodides; arylalkyl halides likebenzyl and phenethyl bromides and others. Water or oil-soluble ordispersible products are thereby obtained. Examples of acids which maybe employed to form pharmaceutically acceptable acid addition saltsinclude such inorganic acids as hydrochloric acid, hydrobromic acid,sulphuric acid and phosphoric acid and such organic acids as oxalicacid, maleic acid, succinic acid and citric acid.

As used herein, the terms “pharmaceutically acceptable”,“physiologically tolerable” and grammatical variations thereof as theyrefer to compositions, carriers, diluents and reagents, are usedinterchangeably and represent that the materials are capable ofadministration to or upon a mammal with a minimum of undesirablephysiological effects such as nausea, dizziness, gastric upset and thelike. The preparation of a pharmacological composition that containsactive ingredients dissolved or dispersed therein is well understood inthe art and need not be limited based on formulation. Typically suchcompositions are prepared as injectables either as liquid solutions orsuspensions, however, solid forms suitable for solution, or suspensions,in liquid-prior to use can also be prepared. The preparation can also beemulsified.

The active ingredient can be mixed with excipients which arepharmaceutically acceptable and compatible with the active ingredientand in amounts suitable for use in the therapeutic-methods describedherein. Suitable excipients include, for example, water, saline,dextrose, glycerol, ethanol or the like and combinations thereof. Inaddition, if desired, the composition can contain minor amounts ofauxiliary substances such as wetting or emulsifying agents, pH bufferingagents and the like which enhance the effectiveness of the activeingredient.

The amount of peptide analogue of the present invention in thepharmaceutical composition of the present invention will depend upon thenature and severity of the condition being treated, on the nature ofprior treatments which the patient has undergone, and on a variety ofother factors, including the type of injury, the age, weight, sex,medical condition of the individual. Ultimately, the attending physicianwill decide the amount of the analogue with which to treat eachindividual patient. Initially, the attending physician will administerlow doses of peptide analogue and observe the patient's response. Largerdoses of peptide analogue may be administered until the optimaltherapeutic effect is obtained for the patient, and at that point thedosage is not increased further.

Additional guidance on methods of determining dosages can be found instandard references, for example, Spilker, Guide to Clinical Studies andDeveloping Protocols, Raven Press Books, Ltd., New York, 1984, pp. 7-13and 54-60; Spilker, Guide to Clinical Trials, Raven Press, Ltd., NewYork, 1991, pp. 93-101; Craig et al., Modern Pharmacology, 2d ed.,Little Brown and Co., Boston, 1986, pp. 127-133; Speight, Avery's DrugTreatment: Principles and Practices of Clinical Pharmacology andTherapeutics, 3d ed., Williams and Wilkins, Baltimore, 1987, pp. 50-56;Tallarida et al., Principles in General Pharmacology, Springer-Verlag,New York, 1998, pp. 18-20; and Olson, Clinical Pharmacology MadeRidiculously Simple, MedMaster, Inc., Miami, 1993, pp. 1-5.

EXAMPLES Example 1 Preparation of N-Terminally Modified GIP andAnalogues Thereof

The N-terminal modification of GIP is essentially a three step process.Firstly, GIP is synthesized from its C-terminal (starting from aFmoc-Gln (Trt)-Wang resin (Calbiochem Novabiochem, Beeston, Nottingham,UK) up to the penultimate N-terminal amino-acid (Ala²) on an automatedpeptide synthesizer (Applied Biosystems, California, USA). Thesynthesis-follows standard Fmoc peptide chemistry protocols. Secondly,the N-terminal amino acid of native GIP (Tyr) is added to a manualbubbler system as a Fmoc-protected Tyr(tBu)-Wang resin. This amino acidis deprotected at its N-terminus (piperidine in DMF (20% v/v)) andallowed to react with a high concentration of glucose (glycation, underreducing conditions with sodium cyanoborohydride), acetic anhydride(acetylation), pyroglutamic acid (pyroglutamyl) etc. for up to 24 hoursas necessary to allow the reaction to go to completion. The completenessof reaction is monitored using the ninhydrin test which determines thepresence of available free a-amino groups. Thirdly (once the reaction iscomplete), the now structurally modified Tyr is cleaved from the Wangresin (95% TFA, and 5% of the appropriate scavengers. N. B. Tyr isconsidered to be a problematic amino acid and may need specialconsideration) and the required amount of N-terminally modified-Tyrconsequently added directly to the automated peptide synthesiser, whichwill carry on the synthesis, thereby stitching the N-terminallymodified-Tyr to the a-amino of GIP (Ala²), completing the synthesis ofthe GIP analogue. This peptide is cleaved off the Wang resin (as above)and then worked up using the standard Buchner filtering, precipation,rotary evaporation and drying techniques.

Example 2 Preparation of Tyr¹-Glucitol GIP and its Properties In Vivo

The following example investigates preparation of Tyr¹ glucitol GIPtogether with evaluation of its antihyperglycemic and insulin-releasingproperties in vivo. The results clearly demonstrate that this novel GIPanalogue exhibits a substantial resistance to aminopeptidase degradationand increased glucose lowering activity compared with the native GIP.

Research Design and Methods

Materials. Human GIP was purchased from the American Peptide Company(Sunnyvale, Calif., USA). HPLC grade acetonitrile was obtained fromRathburn (Walkersburn, Scotland). Sequencing grade trifluoroacetic acid(TFA) was obtained from Aldrich (Poole, Dorset, UK). All other chemicalspurchased including dextran T-70, activated charcoal, sodiumcyanoborohydride and bovine serum albumin fraction V were from Sigma(Poole, Dorset, UK). Diprotin A (DPA) was purchased fromCalbiochem-Novabiochem (UK) Ltd. (Beeston, Nottingham, UK) and ratinsulin standard for RIA was obtained from Novo Industria (Copenhagen,Denmark). Reversed-phase Sep-Pak cartridges (C-18) were purchased fromMillipore-Waters (Milford, Mass., USA). All water used in theseexperiments was purified using a Milli-Q, Water Purification System(Millipore Corporation, Milford, Mass., USA).

Preparation of Tyr¹-glucitol GIP. Human GIP was incubated with glucoseunder reducing conditions in 10 mmol/l sodium phosphate buffer at pH 7.4for 24 hours. The reaction was stopped by addition of 0.5 mol/l aceticacid (30 μl) and the mixture applied to a Vydac (C18)(4.6×250 mm)analytical HPLC column (The Separations Group, Hesperia, Calif., USA)and gradient elution conditions were established using aqueous/TFA andacetonitrile/TFA solvents. Fractions corresponding to the glycated peakswere pooled, taken to dryness under vacuum using an AES 1000 Speed-Vacconcentrator (Life Sciences International, Runcorn, UK) and purified tohomogeneity on a Supelcosil (C-8) (4.6×150 mm) column (Supelco Inc.,Poole, Dorset, UK).

Degradation of GIP and Tyr¹-glucitol GIP by DPP IV. HPLC-purified GIP orTyr¹-glucitol GIP were incubated at 37° C. with DPP-IV (5 mU) forvarious time periods in a reaction mixture made up to 500 μl with 50mmol/l triethanolamine-HC 1, pH 7.8 (final peptide concentration 1mmol/l). Enzymatic reactions were terminated after 0, 2, 4 and 12 hoursby addition of 5 μl of 10% (v/v) TFA/water. Samples were made up to afinal volume of 1.0 ml with 0.12% (v/v) TFA and stored at −20° C. priorto HPLC analysis.

Degradation of GIP and Tyr¹-glucitol GIP by human plasma. Pooled humanplasma (20 μl) taken from six healthy fasted human subjects wasincubated at 37° C. with GIP or Tyr¹-glucitol GIP (10 μg) for 0 and 4hours in a reaction mixture made up to 500 μl, containing 50 mmol/ltriethanolamine/HCL buffer pH 7.8. Incubations for 4 hours were alsoperformed in the presence of diprotin A (5 mU). The reactions wereterminated by addition of 5 μl of TFA and the final volume adjusted to1.0 ml using 0.1% v/v TFA/water. Samples were centrifuged (13,000 g, 5minutes) and the supernatant applied to a C-18 Sep-Pak cartridge(Millipore-Waters) which was previously primed and washed with 0.1%(v/v) TFA/water. After washing with 20 ml 0.12% TFA/water, boundmaterial was released by elution with 2 ml of 80% (v/v)acetonitrile/water and concentrated using a Speed-Vac concentrator(Runcorn, UK). The volume was adjusted to 11.0 ml with 0.12% (v/v)TFA/water prior to HPLC purification.

HPLC analysis of degraded GIP and Tyr¹-glucitol GIP. Samples wereapplied to a Vydac C-18 widepore column equilibriated with 0.12% (v/v)TFA/H₂O at a flow rate of 1.0 mil/minute. Using 0.1% (v/v) TFA in 70%acetonitrile/H₂O, the concentration of acetonitrile in the elutingsolvent was raised from 0% to 31.5% over 15 min, to 38.5% over 30minutes and from 38.5% to 70% over 5 minutes, using linear gradients.The absorbance was monitored at 206 nm and peak areas evaluated using amodel 2221 LKB integrator. Samples recovered manually were concentratedusing a Speed-Vac concentrator.

Electrospray ionization mass spectrometry (ESI-MS). Samples for ESI-MSanalysis containing intact and degradation fragments of GIP (from DPP IVand plasma incubations) as well as Tyr¹-glucitol GIP, were furtherpurified by HPLC. Peptides were dissolved (approximately 400 pmol) in100 μl of water and applied to the LCQ benchtop mass spectrometer(Finnigan MAT, Hemel Hempstead, UK) equipped with a microbore C-18 HPLCcolumn (150×2.0 mm, Phenomenex, Ltd., Macclesfield, UK). Samples (30 μldirect loop injection) were injected at a flow rate of 0.2 ml/min, underisocratic conditions 35% (v/v) acetonitile/water. Mass spectra wereobtained from the quadripole ion trap mass analyzer and recorded.Spectra were collected using full ion scan mode over the mass-to-charge(m/z) range 150-2000. The molecular masses of GIP and related structureswere determined from ESI-MS profiles using prominent multiple chargedions and the following equationM _(r) =iM _(i) −iM _(h)

-   -   where M_(r)=molecular mass; M_(i)=m/z ratio; i=number of        charges; M_(h)=mass of a proton.

In vivo biological activity of GIP and Tyr¹-glucitol GIP. Effects of GIPand Tyr¹-glucitol GIP on plasma glucose and insulin concentrations wereexamined using 10-12 week old male Wistar rats. The animals were housedindividually in an air conditioned room and 22±2° C. with a 12 hourlight/12 hour dark cycle. Drinking water and a standard rodentmaintenance diet (Trouw Nutrition, Belfast, Northern Ireland) weresupplied ad libitum. Food was withdrawn for an 18 hour period prior tointraperitoneal injection of glucose alone (18 mmol/kq body weight) orin combination with either GIP or Tyr¹-glucitol GIP (10 nmol/kg). Testsolutions were administered in a final volume of 8 ml/kg body weight.Blood samples were collected at 0, 15, 30 and 60 minutes from the cuttip of the tail of conscious rats into chilled fluoride/heparinmicrocentrifuge tubes (Sarstedt, Numbrecht, Germany). Samples werecentrifuged using a Beckman microcentrifuge for about 30 seconds at13,000 g. Plasma samples were aliquoted and stored at −20° C. prior toglucose and insulin determinations. All animal studies were done inaccordance with the Animals (Scientific Procedures) Act 1986.

Analyses. Plasma glucose was assayed by an automated glucose oxidaseprocedure using a Beckman Glucose Analyzer II [33]. Plasma insulin wasdetermined by dextran charcoal radioimmunoassay as described previously[34]. Incremental areas under plasma glucose and insulin area under thecurve (AUC) were calculated using a computer program (CAREA) employingthe trapezoidal rule [35] with baseline subtraction. Results areexpressed as mean±SEM and values were compared using the Student'sunpaired t-test. Groups of data were considered to be significantlydifferent if P<0.05.

Degradation of GIP and Tyr¹-glucitol GIP by DPP IV. FIG. 1 illustratesthe typical peak profiles obtained from the HPLC separation of theproducts obtained from the incubation of GIP (FIG. 1 a) or Tyr¹-glucitolGIP (FIG. 1 b) with DPP IV for 0, 2, 4 and 12 hours. The retention timesof GIP and Tyr¹-glucitol GIP at t=0 were 21.93 minutes and 21.75 minutesrespectively. Degradation of GIP was evident after 4 hours incubation(54% intact), and by 12 hours the majority (60%) of intact GIP wasconverted to the single product with a retention time of 21.61 minutes.Tyr¹-glucitol GIP remained almost completely intact throughout 2-12hours incubation. Separation was on a Vydac C-18 column using lineargradients of 0% to 31.5% acetonitrile over 15 minutes, to 38.5% over 30minutes and from 38.5 to 70% acetonitrile over 5 minutes.

Degradation of GIP and Tyr¹-glucitol GIP by human plasma. FIG. 2 shows aset of typical HPLC profiles of the products obtained from theincubation of GIP or Tyr¹-glucitol GIP with human plasma for 0 and 4hours. GIP (FIG. 2 a) with a retention time of 22.06 minutes was readilymetabolised by plasma within 4 hours incubation giving rise to theappearance of a major degradation peak with a retention time of 21.74minutes. In contrast, the incubation of Tyr¹-glucitol GIP under similarconditions (FIG. 2 b) did not result in the formation of any detectabledegradation fragments during this time with only a single peak beingobserved with a retention time of 21.77 minutes. Addition of diprotin A,a specific inhibitor of DPP IV, to GIP during the 4 hours incubationcompletely inhibited degradation of the peptide by plasma. Peakscorresponding with intact GIP, GIP (3-42) and Tyr¹-glucitol GIP areindicated. A major peak corresponding to the specific DPP IV inhibitortripeptide DPA appears in the bottom peanels with retention time of16-29 minutes.

Identification of GIP degradation fragments by ESI-MS. FIG. 3 shows themonoisotopic molecular masses obtained for GIP (FIG. 3A), Tyr¹-glucitolGIP (FIG. 3B) and the major plasma degradation fragment of GIP (FIG. 3C)using ESI-MS. The peptides analyzed were purified from plasmaincubations as shown in FIG. 2. Peptides were dissolved (approximately400 pmol) in 100 μl of water and applied to the LC/MS equipped with amicrobore C-18 HPLC column. Samples (30%1 direct loop injection) wereapplied at a flow rate of 0.2 ml/min, under isocratic conditions 35%acetonitrile/water. Mass spectra were recorded using a quadripole iontrap mass analyzer. Spectra were collected using full ion scan mode overthe mass-to-charge (m/z) range 150-2000. The molecular masses (M_(r)) ofGIP and related structures were determined from ESI-MS profiles usingprominent multiple charged ions and the following equationM_(r)=iM_(i)−iM_(h). The exact molecular mass (M_(r)) of the peptideswere calculated using the equation M_(r)=iM_(i)−iM_(h) as defined abovein Research Design and Methods. After spectral averaging was performed,prominent multiple charges species (M+3H)³⁺ and (M+4H)⁴⁺ were detectedfrom GIP at m/z 1661.6 and 1246.8, corresponding to intact M_(r)4981.8and 4983.2 Da, respectively (FIG. 3A). Similarly, for Tyr¹-glucitol GIP((M+4H)⁴⁺ and (M+5H)⁵⁺) were detected at m/z 1287.7 and 1030.3,corresponding to intact molecular masses of M_(r) 5146.8 and 5146.5 Da,respectively (FIG. 3B). The difference between the observed molecularmasses of the quadruply charged GIP and the N-terminally modified GIPspecies (163.6 Da) indicated that the latter peptide contained a singleglucitol adduct corresponding to Tyr¹-glucitol GIP. FIG. 3C shows theprominent multiply charged species (M+3H)³⁺ and (M+4H)⁴⁺ detected fromthe major fragment of GIP at m/z 1583.8 and 1188.1, corresponding tointact M_(r) 4748.4 and 4748 Da, respectively (FIG. 3C). Thiscorresponds with the theoretical mass of the N-terminally truncated formof the peptide GIP(3-42). This fragment was also the major degradationproduct of DPP IV incubations (data not shown).

Effects of GIP and Tyr¹-glucitol GIP on plasma glucose homeostasis.FIGS. 4 and 5 show the effects of intraperitoneal (ip) glucose alone (18mmol/kg) (control group), and glucose in combination with GIP orTyr¹-glucitol GIP (10 nmol/kg) on plasma glucose and insulinconcentrations.

FIG. 4A shows plasma glucose concentrations after i.p. glucose alone (18mmol/kg) (control group), or glucose in combination with either GIP ofTyr¹-glucitol GIP (10 nmol/kg). The time of injection is indicated bythe arrow (O minutes). FIG. 4B shows plasma glucose AUC values for 0-60minutes post injection. Values are mean±SEM for six rats. **P<0.01,***P<0.001 compared with GIP and Tyr¹⁻glucitol GIP; †P<0.05, ††P<0.01compared with non-glucated GIP. FIG. 5A shows plasma insulinconcentrates after i.p. glucose along (18 mmol/kg) (control group), orglucose in combination with either with GIP or glycated GIP (10nmol/kq). The time of injection is indicated by the arrow. FIG. 5B showsplasma insulin AUC values were calculated for each of the 3 groups up to90 minutes post injection. The time of injection is indicated by thearrow (O minutes). Plasma insulin AUC values for 0-60 minutes postinjection. Values are mean±SEM for six rats. *P<0.05, **P<0.001 comparedwith GIP and Tyr¹⁻glucitol GIP; †P<0.05, ††P<0.01 compared withnon-glycated GIP.

Compared with the control group, plasma glucose concentrations and areaunder the curve (AUC) were significantly lower following administrationof either GIP or Tyr¹-glucitol GIP (FIGS. 4A, B). Furthermore,individual values at 15 and 30 minutes together with AUC weresignificantly lower following administration of Tyr¹-glucitol GIP ascompared to GIP. Consistent with the established insulin-releasingproperties of GIP, plasma insulin concentrations of both peptide-treatedgroups were significantly raised at 15 and 30 minutes compared with thevalues after administration of glucose alone (FIG. 5A). The overallinsulin responses, estimated as AUC were also significantly greater forthe two peptide-treated groups (FIG. 5B). Despite lower prevailingglucose concentrations than the GIP-treated group, plasma insulinresponse, calculated as AUC, following Tyr¹-glucitol GIP wassignificantly greater than after GIP (FIG. 5B). The significantelevation of plasma insulin at 30 minutes is of particular note,suggesting that the insulin-releasing action of Tyr¹-glucitol GIP ismore protracted than GIP even in the face of a diminished glycemicstimulus (FIGS. 4A, 5A).

Example 3 Additional N-Terminal Structural Modifications of GIP

This example further looked at the ability of additional N-terminalstructural modifications of GIP in preventing inactivation by DPP and inplasma and their associated increase in both the insulin-releasingpotency and potential therapeutic value. Native human GIP, glycated GIP,acetylated GIP and a number of GIP analogues with N-terminal amino acidsubstitutions were tested.

Materials and Methods. High-performance liquid chromatography (HPLC)grade acetonitrile was obtained from Rathburn (Walkersburn, Scotland).Sequencing grade trifluoroacetic acid (TFA) was obtained from Aldrich(Poole, Dorset, UK). Dipeptidyl peptidase IV was purchased from Sigma(Poole, Dorset, UK), and Diprotin A was purchased from CalbiochemNovabiochem (Beeston, Nottingham, UK). RPMI 1640 tissue culture medium,foetal calf serum, penicillin and streptomycin were all purchased fromGibco (Paisley, Strathclyde, UK). All water used in these experimentswas purified using a Milli-Q, Water Purification System (Millipore,Milford, Mass., USA). All other chemicals used were of the highestpurity available.

Synthesis of GIP and N-terminally modified GIP analogues. GIP,GIP(Abu²), GIP(Sar²), GIP(Ser²), GIP(Gly²) and GIP(Pro³) weresequentially synthesized on an Applied Biosystems automated peptidesynthesizer (model 432 A) using standard solid-phase Fmoc procedure,starting with an Fmoc-Gln-Wang resin. Following cleavage from the resinby trifluoroacetic acid:water, thioanisole, ethanedithiol (90/2.5/5/2.5,a total volume of 20 ml/g resin), the resin was removed by filtrationand the filtrate volume was decreased under reduced pressure. Drydiethyl ether was slowly added until a precipitate was observed. Theprecipitate was collected by low-speed centrifugation, resuspended indiethyl ether and centrifuged again, this procedure being carried out atleast five times. The pellets were then dried in vacuo and judged pureby reversed-phase HPLC on a Waters Millennium 2010 chromatography system(Software version 2.1.5.). N-terminal glycated and acetylated GIP wereprepared by minor modification of a published method.

Electrospray ionization-mass spectrometry (ESI-MS) was carried out asdescribed in Example 2. Degradation of GIP and novel GIP analogues byDPP IV and human plasma was carried out as described in Example 2.

Culture of insulin secreting cells. BRIN-BD11 cells [30] were culturedin sterile tissue culture flasks (Corning, Glass Works, UK) usingRPMI-1640 tissue culture medium containing 10% (v/v) foetal calf serum,1% (v/v) antibiotics (100 U/ml penicillin, 0.1 mg/ml streptomycin) and11.1 mM glucose. The cells were maintained at 37° C. in an atmosphere of5% CO₂ and 95% air using a LEEC incubator (Laboratory TechnicalEngineering, Nottingham, UK).

Acute tests for insulin secretion. Before experimentation, the cellswere harvested from the surface of the tissue culture flasks with theaid of trypsin/EDTA (Gibco), seeded into 24-multiwell plates (Nunc,Roskilde, Denmark) at a density of 1.5×10⁵ cells per well, and allowedto attach overnight at 37° C. Acute tests for insulin release werepreceded by 40 minutes pre-incubation at 37° C. in 1.0 ml Krebs Ringerbicarbonate buffer (115 mM NaCl, 4.7 mM KCl, 1.28 mM CaCl₂, 1.2 mMKH₂PO₄, 1.2 mM MgSO₄, 10 mM NaHCO₃, 5 g/l bovine serum albumin, pH 7.4)supplemented with 1.1 mM glucose. Test incubations were performed (n=12)at two glucose concentrations (5.6 mM and 16.7 mM) with a range ofconcentrations (10⁻¹³ to 10⁻⁸ M) of GIP or GIP analogues. After 20minutes incubation, the buffer was removed from each well and aliquots(200 μl) were used for measurement of insulin by radioimmunoassay [31].

Statistical analysis. Results are expressed as mean±S.E.M. and valueswere compared using the Student's unpaired t-test. Groups of data wereconsidered to be significantly different if P<05.

Structural identification of GIP and GIP analogues by ESI-MS. Themonoisotopic molecular masses of the peptides were determined usingESI-MS. After spectral averaging was performed, prominent multiplecharged species (M+3H)³⁺ and (M+4H)⁴⁺ were detected for each peptide.Calculated molecular masses confirmed the structural identity ofsynthetic GIP and each of the N-terminal analogues.

Degradation of GIP and novel GIP analogues by DPP-IV. FIGS. 6-11illustrate the typical peak profiles obtained from the HPLC separationof the reaction products obtained from the incubation of GIP, GIP(Abu²),GIP(Sar²), GIP(Ser²), glycated GIP and acetylated GIP with DPP IV, for0, 2, 4, 8 and 24 hours. The results summarized in Table 1 indicate thatglycated GIP, acetylated GIP, GIP(Ser²) are GIP(Abu²) more resistantthan native GIP to in vitro degradation with DPP IV. From these dataGIP(Sar²) appears to be less resistant. TABLE 1 Percent intact peptideremaining after incubation with DPPIV. % Intact peptide remaining aftertime (h) Peptide 0 2 4 8 24 GIP 1-42 100 52 ± 1 23 ± 1 0 0 Glycated GIP100 100 100 100 100 GIP (Abu²) 100 38 ± 1 28 ± 2 0 0 GIP (Ser²) 100 77 ±2 60 ± 1 32 ± 4 0 GIP (Sar²) 100 28 ± 2 8 0 0 N-Acetyl-GIP 100 100 100100

Table represents the percentage of intact peptide (i.e., GIP 1-42)relative to the major degradation product GIP 3-42. Values were takenfrom HPLC traces performed in triplicate and the mean and S.E.M. valuescalculated. DPA is diprotin A, a specific inhibitor of DPPIV.

Degradation of GIP and GIP analogues by human plasma. FIGS. 12-16 show arepresentative set of HPLC profiles obtained from the incubation of GIPand GIP analogues with human plasma for 0, 2, 4, 8 and 24 hours.Observations were also made after incubation for 24 hours in thepresence of DPA. These results are summarized in Table 2 are broadlycomparable with DPP IV incubations, but conditions which more closelymirror in vivo conditions are less enzymatically severe. GIP was rapidlydegraded by plasma. In comparison, all analogues tested exhibitedresistance to plasma degradation, including GIP(Sar²) which from DPP IVdata appeared least resistant of the peptides tested. DPA substantiallyinhibited degradation of GIP and all analogues tested with completeabolition of degradation in the cases of GIP(Abu²), GIP(Ser²) andglycated GIP. This indicates that DPP IV is a key factor in the in vivodegradation of GIP. TABLE 2 Percent intact peptide remaining afterincubation with human plasma. % Intact peptide remaining afterincubations with human plasma Peptide 0 2 4 8 24 DPA GIP 1-42 100 52 ± 123 ± 1 0 0 68 ± 2 Glycated GIP 100 100 100 100 100 100 GIP (Abu²) 100 38± 1 28 ± 2 0 0 100 GIP (Ser²) 100 77 ± 2 60 ± 1 32 ± 4 0 63 ± 3 GIP(Sar²) 100 28 ± 2 8 0 0 100

Table represents the percentage of intact peptide (i.e., GIP 1-42)relative to the major degradation product GIP 3-42. Values were takenfrom HPLC traces performed in triplicate and the mean and S.E.M. valuescalculated. DPA is diprotin A, a specific inhibitor of DPPIV.

Dose-dependent effects of GIP and novel GIP analogues on insulinsecretion. FIGS. 17-30 show the effects of a range of concentrations ofGIP, GIP(Abu²), GIP(Sar²), GIP(Ser 2), acetylated GIP, glycated GIP,GIP(Gly²) and GIP(Pro³) on insulin secretion from BRIN-BD11 cells at 5.6and 16.7 mM glucose. Native GIP provoked a prominent and dose-relatedstimulation of insulin secretion. Consistent with previous studies [28],the glycated GIP analogue exhibited a considerably greaterinsulinotropic response compared with native peptide. N-terminalacetylated GIP exhibited a similar pattern and the GIP(Ser 2) analoguealso evoked a strong response. From these tests, GIP(Gly²) and GIP(Pro³)appeared to be the least potent analogues in terms of insulin release.Other stable analogues tested, namely GIP(Abu²) and GIP(Sar²), exhibiteda complex pattern of responsiveness dependent on glucose concentrationand dose employed. Thus very low concentrations were extremely potentunder hyperglycemic conditions (16.7 mM glucose). This suggests thateven these analogues may prove therapeutically useful in the treatmentof type 2 diabetes where insulinotropic capacity combined with in vivodegradation dictates peptide potency.

Example 4 Glu³ Substituted GIP Improves Obesity-Related InsulinResistance and Associated Glucose Intolerance

This example examines GIP receptor antagonism and obesity-relatedinsulin resistance and associated glucose intolerance using aGlu³-substituted form of GIP, namely, (Pro³)GIP.

Cell lines and animals. In vitro insulin secretion was evaluated usingthe clonal pancreatic beta-cell line, BRIN-BD11 (McClenaghan, N. H. etal., 1996, Diabetes 45:1132-1140). In vitro cyclic AMP generation wasmeasured using Chinese hamster lung (CHL) fibroblast cells stablytransfected with the human GIP receptor (Gremlich, S. et al., 1995,Diabetes 44:1202-1208). In vivo studies were conducted in 8-12 week-oldobese diabetic ob/ob mice (Bailey C. J. et al., 1982, Int. J. Obesity6:11-21) and normal control mice.

Peptide synthesis and characterisation. Glu³-substituted analogues weresequentially synthesised on an Applied Biosystems automated peptidesynthesiser (Model 432 A) using standard solid-phase Fmoc peptidechemistry (Fields, G. B. et al., 1990, Int. J. Pept. Protein Res.35:161-214), from a pre-loaded Fmoc-Gln-Wang resin. The syntheticpeptides were judged pure by reversed-phase HPLC on a Waters Millenium2010-chromatography system (Software version 2.1.5). The molecularmasses of the purified peptide analogues were determined using MatrixAssisted Laser Desorption ionisation-Time of Flight (MALDI-TOF) massspectrometry. Samples were dissolved in 10 W H₂O (approximately 40pmol/l), placed on a stainless steel sample plate and allowed to dry atroom temperature. Samples were then mixed with a matrix solution (10mg/ml solution of α-cyano-4-hydroxycinnamic acid) inacetonitrile/ethanol (1/1) and allowed to dry at room temperature. Themolecular masses were then recorded as mass-to-charge (m/z) ratio versusrelative peak intensity and compared using theoretical values on aVoyager-DE BioSpectrometry Workstation (PerSeptive Biosystems,Framingham, Mass., USA).

Tissue culture. Chinese hamster lung (CHL) fibroblast cells stablytransfected with the human GIP receptor were cultured in DMEM tissueculture medium containing 10% (v/v) foetal bovine serum, 1% (v/v)antibiotics (100 U/ml penicillin, 0.1 mg/ml streptomycin). BRIN-BD11cells were cultured using RPMI-1640 tissue culture medium containing 10%(v/v) foetal bovine serum, 1% (v/v) antibiotics (100 U/ml penicillin,0.1 mg/ml streptomycin). Cells were maintained in sterile tissue cultureflasks (Corning Glass Works, Sunderland, UK) at 37° C. in an atmosphereof 5% CO₂ and 95% air using an LEEC incubator (Laboratory TechnicalEngineering, Nottingham, UK).

Acute studies of insulin release. Insulin release from BRIN-BD11 cellswas determined using cell monolayers (McClenaghan, N. H. et al., 1996,Diabetes 45:1132-1140). Cells were harvested with the aid oftrypsin/EDTA (Gibco), seeded into 24-multiwell plates (Nunc, Roskilde,Denmark) at a density of 1.0×10⁵ cells per well, and allowed to attachovernight at 37° C. Prior to acute test, cells were preincubated for 40minutes at 37° C. in 1.0 ml Krebs Ringer bicarbonate buffer (115 mMNaCl, 4.7 mM KCl, 1.28 mM CaCl₂, 1.2 mM KH₂PO₄, 1.2 mM MgSO₄, 10 mMNaHCO₃, 0.5% (w/v) bovine serum albumin, pH 7.4) supplemented with 1.1mM glucose. Acute tests for insulin release were performed for 20minutes at 37° C. at 5.6 mM glucose using various concentrations ofGlu³-substituted analogues and GIP(3-42) in the presence of native GIP(10⁻⁷ M) as indicated in the Figures. After incubation, aliquots ofbuffer were removed and stored at −20° C. for insulin radioimmunoassay(Flatt, P. R. et al., 1981, Diabetologia 20:573-577).

Acute studies of cyclic AMP generation. GIP receptor transfected CHLcells were seeded into 12-well plates (Nunc, Roskilde, Denmark) at adensity of 1.0×10⁵ cells per well. The cells were then allowed to growfor 48 hours before being loaded with tritiated adenine (2 ηCi; TRK311,Amersham, Buckinghamshire, UK) and incubated at 37° C. for 6 hours in 1ml DMEM, supplemented with 0.5% (w/v) foetal bovine serum. The cellswere then washed twice with HBS buffer (130 mM NaCl, 20 mM HEPES, 0.9 mMNaHPO₄, 0.8 mM MgSO₄, 5.4 mM KCl, 1.8 mM CaCl₂, 25 mM glucose, 25 μMphenol red, pH 7.4). The cells were then exposed for 10 minutes at 37°C. to forskolin (FSK, 10 μM) or varying concentrations of (Pro³)GIP inthe absence (control) or presence of native GIP (10⁻⁷ M). After removalof the medium, cells were lysed with 1 ml of 5% trichloroacetic acid(TCA) containing 0.1 mM unlabelled cAMP and 0.1 mM unlabelled ATP. Theintracellular tritiated cAMP was then separated on Dowex and aluminaexchange resins as previously described (Widmann, C. et al., 1993, Mol.Pharmacol. 45:1029-1035).

Acute in vivo effects of (Pro³)GIP administration in obese diabeticob/ob mice. Plasma glucose and insulin responses were evaluated using 8-to 12-week old obese diabetic ob/ob mice following intraperitoneal(i.p.) injection of native GIP, (Pro³)GIP (25 nmol/kg body weight) orsaline (0.9% (w/v) NaCl; control) immediately following the combinedinjection of GIP (25 nmol/kg body weight) with glucose (18 mmol/kg bodyweight). All test solutions were administered in a final volume of 8ml/kg body weight. Blood samples were collected from the cut tip of thetail of conscious mice into chilled fluoride/heparin microcentrifugetubes (Sarstedt, Numbrecht, Germany) immediately prior to injection andat 15, 30 and 60 minutes post injection. Blood samples were immediatelycentrifuged using a Beckman microcentrifuge (Beckman Instruments, UK)for 30 seconds at 13000 g and stored at −20° prior to glucose andinsulin determinations.

Acute in vivo effects of (Pro³)GIP on plasma glucose and insulinresponses to feeding in obese diabetic ob/ob mice. Plasma glucose andinsulin responses were evaluated using 8- to 12-week old ob/ob micewhere food was withdrawn for an 18-hour period prior to intraperitonealinjection of saline (0.9% (w/v) NaCl; control) or (Pro³)GIP (25 nmol/kgbody weight). Following injection, the mice were allowed to re-feed for15 minutes. Blood samples were collected from the cut tip of the tail ofconscious mice into chilled fluoride/heparin microcentrifuge tubes(Sarstedt, Numbrecht, Germany) immediately prior to injection and at 15,30, 60 and 120 minutes post injection. Blood samples were immediatelycentrifuged using a Beckman microcentrifuge (Beckman Instruments, UK)for 30 seconds at 13000 g and stored at −20° prior to glucose andinsulin determinations.

Effects of chronic (Pro³)GIP administration on plasma glucose, insulinand glycated HbA_(1c) in obese diabetic ob/ob mice and normal mice.Obese diabetic ob/ob mice and normal control mice aged 8-12 weeks wererandomly divided into groups which received once daily subcutaneousinjections (17:00 h) of either saline (0.9% w/v NaCl) or (Pro³)GIP (25nmol/kg body weight in saline). After 11 days, treatment was ceased.Food intake and body weight were recorded daily. Blood samples werecollected from the cut tip of the tail of conscious mice into chilledfluoride/heparin coated glucose microcentrifuge tubes (Sarstedt,Numbrecht, Germany). Blood samples were immediately centrifuged using aBeckman microcentrifuge (Beckman Instruments, UK) for 30 seconds at13000 g prior to glucose, insulin and HbA_(1c) determinations.

Effects of chronic treatment with (Pro³)GIP on glucose tolerance inob/ob mice and normal mice. Plasma glucose and insulin concentrationswere measured following intraperitoneal administration of glucose (18mmol/kg body weight) in ob/ob and normal mice treated with either saline(0.9% w/v NaCl) or (Pro³)GIP (25 nmol/kg body weight/day) for 11 days.This test was repeated 9 days after cessation of chronic (Pro³)GIPtreatment. Blood samples were collected from the cut tip of the tail ofconscious mice into chilled fluoride/heparin microcentrifuge tubes(Sarstedt, Numbrecht, Germany) immediately prior to injection and at 15,30 and 60 minutes post injection. Blood samples were immediatelycentrifuged using a Beckman microcentrifuge (Beckman Instruments, UK)for 30 seconds at 13000 g and stored at −20° prior to glucose andinsulin determinations.

Effects of chronic treatment with (Pro³)GIP on the glucose loweringeffects of exogenous insulin in ob/ob mice. The glucose lowering effectsof insulin were evaluated by measuring plasma glucose response in 11-daysaline (0.9% w/v NaCl) and (Pro³)GIP (25 nmol/kg body weight/day)treated ob/ob mice following acute intraperitoneal administration ofinsulin (50 U/kg bodyweight). Blood samples were collected from the cuttip of the tail of conscious mice into chilled fluoride/heparinmicrocentrifuge tubes (Sarstedt, Numbrecht, Germany) immediately priorto injection and at 30 and 60 minutes post injection. Blood samples wereimmediately centrifuged using a Beckman microcentrifuge (BeckmanInstruments, UK) for 30 seconds at 13000 g and stored at −20° prior toglucose determination.

Effects of chronic treatment with (Pro³)GIP on pancreatic insulincontent and associated islet hypertrophy in ob/ob mice. Pancreatictissue was excised from non-fasted ob/ob mice after 11 days treatmentwith either saline (0.9% w/v NaCl) or (Pro³)GIP (25 nmol/kg bodyweight/day). Pancreatic samples were individually wrapped in aluminiumfoil and snap frozen in liquid nitrogen. Individual excised pancreaticsamples were then either embedded, sectioned and immunohistochemicallystained for insulin or permeabilised for determination of pancreaticinsulin content.

Determination of HbA_(1c), plasma glucose and insulin concentrations.HbA_(1c) was measured in whole blood by ion-exchange high-performanceliquid chromatography using the Menari HA-8140 kit (BIOMEN, Berkshire,UK). Plasma glucose was assayed by an automated glucose oxidaseprocedure using a Beckman Glucose Analyzer II (Stevens, J. F., 1971,Clinica Chemica Acta 32:199-201) and plasma insulin was determined byRIA (Flatt, P. R. et al., 1981, Diabetologia 20:573-577). Incrementalareas under plasma glucose and insulin curves (AUC) were calculatedusing a computer generated program (CAREA) employing the trapezoidalrule (Burington, R. S., 1973, Handbook of Mathematical Tables andFormulae, New York, McGraw Hill) with baseline subtraction.

Statistical analysis. Results are expressed as means±SEM. Values werecompared using Student's unpaired t-test and groups of data wereconsidered to be significantly different if P<0.05.

Results

GIP-stimulated cyclic AMP production and insulin secretion wereinhibited in dose-dependent fashion by (Pro³)GIP, showing that (Pro³)GIPis a potent functional GIP receptor antagonist.

GIP receptor transfected Chinese hamster lung (CHL) fibroblasts wereincubated with 10⁻² to 10⁻⁶ M(Pro³)GIP in the presence of native GIP(10⁻⁷ M). The results are shown in FIGS. 32A and 32B. FIG. 32A is a linegraph showing ³H-cAMP production as a percent of maximal response(y-axis) with increasing peptide concentration (M) (x-axis). FIG. 32B isa bar graph showing insulin secretion (y-axis) with increasing peptideconcentration (M) (x-axis) for 5.6 mM glucose (control) (white bar), GIP(gray bars), (Pro³)GIP (lined bars) and (Pro³)GIP+GIP(10⁻⁷M) (blackbars). *P<0.05, **P<0.01, ***P<0.001 compared to glucose control.^(ΔΔ)P<0.01, ^(ΔΔΔ)P<0.001 compared with native GIP at the sameconcentration. Values are means±SEM for 3-8 observations.

(Pro³)GIP inhibited GIP-induced cAMP formation with an IC₅₀ value of 2.6μM. Insulin-releasing activity of BRIN-BD11 cells exposed to native GIPand (Pro³)GIP (in the absence and presence of 10⁻⁷ M GIP).

GIP-stimulated insulin secretion was inhibited in a dose-dependentfashion by GIP(3-42), (Hyp³)GIP, (Lys³)GIP, (Tyr³)GIP, (Trp³)GIP, and(Phe³)GIP, as shown in FIGS. 33A through 33F, which are bar charts. FIG.33A shows ³H-cAMP production as a percent of 10⁻⁷M GIP (y-axis) versuslog₁₀ of GIP (10⁻⁷M) (white bar, control) and GIP (10⁻⁷M)+GIP(3-42)(black bars). FIGS. 33B through 33F show insulin secretion (in ng/10⁶cells/20 minutes) (y-axis) as a function of peptide concentration (M)(x-axis) for GIP (10⁻⁷M) (white bar, control) and a Glu³-substitutedform of GIP (black bars), including (Hyp³)GIP (FIG. 33B), (Lys³)GIP(FIG. 33C), (Tyr³)GIP (FIG. 33D), (Trp³)GIP (FIG. 33E), and (Phe³)GIP(FIG. 33F). *P<0.05, **P<0.01 compared to GIP (10⁻⁷ M) control. Valuesare means±SEM for 3-8 observations.

FIGS. 34A through 34D are a set of two line graphs (FIGS. 34A, 34C) andtwo bar graphs (FIGS. 34B, 34D) showing that acute administration of(Pro³)GIP completely antagonises the actions of GIP on glucose tolerance(FIGS. 34A, 34B) and plasma insulin (FIGS. 34C, 34D) responses in obesediabetic ob/ob mice. FIGS. 34A and 34C are line graphs show plasmaglucose levels (FIG. 34A, y-axis) and plasma insulin levels (FIG. 34C,y-axis) over time (x-axis) for glucose (control; ▾), glucose+GIP (♦) andglucose+(GIP+Pro³GIP)) (Δ). FIGS. 34B and 34D are bar graphs showingplasma glucose AUC for glucose alone (white bars), GIP (grey bars) andglucose+(GIP+Pro³GIP)) (black bars).

Plasma glucose and insulin concentrations after i.p. administration ofglucose alone (18 mmol/kg body weight) or in combination with eithernative GIP or native GIP plus (Pro³)GIP (25 nmol/kg body weight). Thetime of injection is indicated by the arrow (0 minutes). Plasma glucoseand insulin AUC values are given for 0-60 minutes post-injection. Valuesare means±SEM for 8 mice. *P<0.05, **P<0.01, ***P<0.001 compared withglucose alone. ^(ΔΔ)P<0.01, ^(ΔΔΔ)P<0.001 compared with native GIP.

Acute administration of (Pro³)GIP completely antagonised theinsulin-releasing action of GIP and the associated improvement ofglucose tolerance in ob/ob mice. Indeed, the glycemic excursionfollowing (Pro³)GIP (Δ) was worse than when glucose was administeredalone (▾).

FIGS. 35A through 35D show the effects of (Pro³)GIP on physiologicalmeal-stimulated insulin release and glycemic excursion in obese diabeticob/ob mice. Plasma glucose and insulin concentrations were measured inmice allowed to re-feed for 15 minutes prior to i.p. administration ofsaline (0.9% (w/v) NaCl) as control or (Pro³)GIP (25 nmol/kg bodyweight). The time of injection is indicated by the arrow (15 minutes).

The results are shown in FIGS. 35A through 35D, which are a set of twoline graphs (FIGS. 35A, 35C) and two bar graphs (FIGS. 35B, 35D). Thefigures show plasma insulin (FIGS. 35A) and plasma glucose (FIG. 35C)over time for saline control (▾) and (Pro³)GIP (⋄), and plasma insulinAUC (FIG. 35B) and plasma glucose AUC (FIG. 35D) for saline control(white bars) and (Pro³)GIP (black bars), respectively. Values aremeans±SEM for 8 mice. *P<0.05, **P<0.01, ***P<0.001 compared with salinealone.

Acute administration of (Pro³)GIP decreased the insulin response tofeeding and worsened the associated glycemic excursion in ob/ob mice.These effects of functional ablation of endogenous GIP by the (Pro³)GIPantagonist are fully consistent with the accepted role of GIP in theregulation of insulin secretion and glycemic excursion followingfeeding.

The effects of chronic administration of (Pro³)GIP for 11 days on plasmaglucose and insulin concentrations of obese diabetic ob/ob mice werealso studied. According to classical thinking and the experimentsdescribed above and the results shown in FIGS. 32-35, functionalablation of endogenous GIP by daily administration of (Pro³)GIP over 11days would be expected to inhibit insulin secretion and cause a markeddeterioration in glucose tolerance.

However, the exact opposite occurred during chronic treatment with(Pro³)GIP in ob/ob mice. This is shown in FIG. 36, which is a set of twobar graphs showing plasma glucose (FIG. 36A) and insulin (FIG. 36B)concentrations after daily subcutaneous administration of saline alone(0.9% (w/v) NaCl; as control; white bars) or (Pro³)GIP (25 nmol/kg bodyweight; black bars) for 11 days. Values are means±SEM for 6 mice and*P<0.05 compared with saline alone. Chronic administration of (Pro³)GIP(black bars) for 11 days decreases plasma glucose and plasma insulinconcentrations of obese diabetic ob/ob mice, relative to controls.

The effects of chronic administration of (Pro³)GIP for 11 days onHbA_(1C), (FIG. 37A), pancreatic insulin content (FIG. 37B) andassociated islet hypertrophy (FIG. 37C) were examined in obese diabeticob/ob mice treated with saline (control, white bars) and (Pro³)GIP wereexamined. HbA_(1c), pancreatic insulin content and average isletdiameter were measured after 11 daily subcutaneous injections of eithersaline alone (white bars) or (Pro³)GIP (25 nmol/kg body weight; blackbars) to obese diabetic ob/ob mice. Values are means±SEM for 6 mice and*P<0.05, ***P<0.001 compared with saline-treated group.

Beneficial effects of chronic (Pro³)GIP administration in ob/ob micewere associated with significant decreases in HbA_(1c) and pancreaticinsulin stores, with partial correction of the marked islet hypertrophyof the ob/ob mutant. There was also an approximate 7% decrease in bodyweight in (Pro 3)GIP-treated ob/ob mice without any change in foodintake. This effect did not achieve significance over the short studyperiod, but this observation clearly suggests that GIP antagonism mayalso have a longer-term anti-obesity action.

The effects of chronic administration of (Pro³)GIP for 11 days onglucose tolerance and plasma insulin in obese diabetic ob/ob mice isshown in FIGS. 38A-38D, which are a set of line graphs (FIGS. 38A, 38C)and bar graphs (FIGS. 38B, 38C) showing plasma glucose levels (FIGS.38A, 38B) and plasma insulin levels (FIGS. 38C, 38D) in obese diabeticob/ob mice treated with saline (control, white) or (Pro³)GIP (black).Plasma glucose and insulin concentrations were measured prior to and atintervals after intraperitoneal administration of glucose (18 mmol/kgbody weight). Arrow indicates time of injection (t=0). Values aremeans±SEM for 6 mice and *P<0.05, **P<0.01, ***P<0.001 compared withsaline-treated group.

After 11 days treatment with (Pro³)GIP, glucose tolerance of ob/ob micewas substantially improved without change of circulating insulin (FIG.38).

FIG. 39 shows the effects of chronic administration of (Pro³)GIP for 11days on insulin sensitivity in obese diabetic ob/ob mice. Plasma glucoseconcentrations of saline and (Pro³)GIP treated ob/ob mice were measuredprior to and at intervals after intraperitoneal administration ofexogenous insulin (50 U/kg body weight; t=0). Values are means±SEM for 6mice and *P<0.05 compared with saline-treated group. As shown in FIG.39, chronic administration of (Pro³)GIP caused a significant improvementof insulin sensitivity.

Interestingly, the beneficial effects of chronic administration of(Pro³)GIP for 11 days in obese diabetic ob/ob mice was reversed 9 daysafter cessation of treatment. This is consistent with a physiologicaleffect, and is shown in FIG. 40. Plasma glucose concentrations weremeasured prior to and after intraperitoneal administration of glucose(18 mmol/kg body weight) for mice that had been treated with saline(control, □) or (Pro³)GIP (▴). Arrow indicates time of injection (t=0).Values are means±SEM for 6.

FIGS. 41A and 41B are a pair of line graphs showing the effects ofchronic administration of (Pro³)GIP for 11 days on glucose tolerance innormal mice. Plasma glucose concentrations were measured prior to andafter intraperitoneal administration of glucose (18 mmol/kg bodyweight). Arrow indicates time of injection (t=0). Values are means±SEMfor 6 and *P<0.05, **P<0.01 compared to saline-treated group.

In total contrast to beneficial actions in ob/ob mice, chronic dailytreatment of normal mice with (Pro³)GIP (Δ) for 11 days resulted in amarked deterioration of glucose tolerance (FIG. 41A) relative tocontrols (▪), which was reversed 9 days after cessation of treatment(FIG. 41B).

Example 5 Chemical Ablation of Gastric Inhibitory Polypeptide ReceptorAction By Daily (Pro³)GIP Administration Improves Glucose Tolerance andAmeliorates Insulin Resistance and Abnormalities of Islet Structure inObesity-Diabetes

Gastric inhibitory polypeptide (GIP) is an important incretin hormonesecreted by endocrine K-cells in response to nutrient ingestion. Thisstudy investigated the effects of chemical ablation of GIP receptor(GIP-R) action on aspects of obesity-diabetes using a stable andspecific GIP-R antagonist, (Pro³)GIP. Young adult ob/ob mice receivedonce daily i.p. injections of saline vehicle or (Pro³)GIP over an 1′-dayperiod. Non-fasting plasma glucose levels and the overall glycemicexcursion (AUC) to a glucose load were significantly reduced (1.6-fold;P<0.05) in (Pro³)GIP-treated mice compared to controls. GIP-R ablationalso significantly lowered overall plasma glucose (1.4-fold; P<0.05) andinsulin (1.5-fold; P<0.05) responses to feeding. These changes wereassociated with significantly enhanced (1.6-fold; P<0.05) insulinsensitivity in the (Pro³)GIP-treated group. Daily injection of (Pro³)GIPreduced pancreatic insulin content (1.3-fold; P<0.05) and partiallycorrected the obesity-related islet hypertrophy and beta cellhyperplasia of ob/ob mice. These comprehensive beneficial effects of(Pro³)GIP were reversed following 9 days cessation of treatment and wereindependent of food intake and body weight, which were unchanged. Thesestudies highlight a role for GIP in obesity-related glucose intoleranceand emphasize the potential of specific GIP-R antagonists as a new classof drugs for the alleviation of insulin resistance and treatment of type2 diabetes.

Research Design And Methods

Animals. Obese diabetic (ob/ob) mice derived from the colony maintainedat Aston University, UK (Bailey, C. J., et al., 1982, Int. J. Obes.6:11-21) were used at 12-16 weeks of age. Animals were age-matched,divided into groups and housed individually in an air-conditioned roomat 22±2° C. with a 12 hour light: 12 hour dark cycle. Drinking water anda standard rodent maintenance diet (Trouw Nutrition, Cheshire, UK) werefreely available. All animal experiments were carried out in accordancewith the UK Animals (Scientific Procedures) Act 1986. No adverse effectswere observed following administration of (Pro³)GIP.

Synthesis, purification and characterization of (Pro³)GIP. (Pro³)GIP wassequentially synthesized on an Applied Biosystems automated peptidesynthesizer (Model 432 A). (Pro³)GIP was purified by reversed-phase HPLCon a Waters Millenium 2010 chromatography system (Software version2.1.5) and subsequently characterized using electrospray ionization massspectrometry (ESI-MS).

Experimental protocols for ob/ob mouse studies. Initially, extendedbiological activity of (Pro³)GIP was examined in 18-hour fasted ob/obmice 4 hours after administration. Thereafter, over an 11-day period,mice received once daily i.p. injections (17:00 hours) of either salinevehicle (0.9% (w/v), NaCl) or (Pro³)GIP (25 nmol/kg body wt). During asubsequent 9-day period, observations were continued followingdiscontinuation of (Pro³)GIP administration. Food intake and body weightwere recorded daily whilst plasma glucose and insulin concentrationswere monitored at intervals of 2-6 days. Whole blood for the measurementof glycated hemoglobin was taken on days 11 and 20. Intraperitonealglucose tolerance (18 mmol/kg body wt), metabolic response to native GIP(25 nmol/kg body wt) and insulin sensitivity (50 U/kg body wt) testswere performed on days 11 and 20. Mice fasted for 18 hours were used toexamine the metabolic response to 15 minutes feeding. In a separateseries, pancreatic tissues were excised at the end of the 11-daytreatment period or 9 days following discontinuation of (Pro³)GIP andprocessed for immunohistochemistry or measurement of insulin followingextraction with 5 ml/g of ice-cold acid ethanol (750 ml ethanol, 235 mlwater, 15 ml concentrated HCl). Blood samples taken from the cut tip ofthe tail vein of conscious mice at the times indicated in the Figureswere immediately centrifuged using a Beckman microcentrifuge (BeckmanInstruments, UK) for 30 seconds at 13,000 g. The resulting plasma wasthen aliquoted into fresh Eppendorf tubes and stored at −20° C. prior toglucose and insulin determinations.

Biochemical analysis. Plasma glucose was assayed by an automated glucoseoxidase procedure (Stevens, J. F., 1971, Clin. Chem. Acta 32:199-201)using a Beckman Glucose Analyzer II (Beckman Instruments, Galway,Ireland). Plasma and pancreatic insulin were assayed by a modifieddextran-coated charcoal radioimmunoassay (Flatt, P. R. et al., 1981,Diabetologia 20:573-577). Glycated hemoglobin was determined usingcation-exchange columns (Sigma, Poole, Dorset, UK) with measurement ofabsorbance (415 nm) in wash and eluting buffer using a VersaMaxMicroplate Spectrophotometer (Molecular Devices, Wokingham, Berkshire,UK).

Immunocytochemistry. Tissue fixed in 4% paraformaldehyde/PBS andembedded in paraffin was sectioned at 8 μm. After de-waxing, sectionswere incubated with blocking serum (Vector Laboratories, CA, USA) priorto exposure to insulin antibody. Tissue samples were then incubatedconsecutively with secondary biotinylated universal, pan-specificantibody (Vector Laboratories, CA, USA) and streptavidin/peroxidasepreformed complex (Vector Laboratories, CA, USA). Following washing, thestained pancreatic tissue was counterstained with hematoxylin (BDHChemicals, Dorset, UK) and then plunged into acid methanol (500 mlmethanol, 500 ml H₂O and 2.5 ml concentrated HCl) prior to dehydrationand mounting in Depex (BDH Chemicals, Dorset, UK). The stained slideswere viewed under a microscope (Nikon Eclipse E2000, DiagnosticInstruments Incorporated, Michigan, USA) attached to a JVC camera ModelKY-F55B (JVC, London, UK) and analyzed using Kromoscan imaging software(Kinetic Imaging Limited, Faversham, Kent, UK). The average number anddiameter of every islet in each section was estimated in a blindedmanner using an eyepiece graticule calibrated with a stage micrometer(Graticules Limited, Tonbridge, Kent, UK). The longest and shortestdiameters of each islet were determined with the graticule. Half of thesum of these two values was then considered to be the average isletdiameter. Approximately 60-70 random sections were examined from thepancreas of each mouse.

Statistics. Results are expressed as mean±SEM. Data were compared usingANOVA, followed by a Student-Newman-Keuls post hoc test. Area under thecurve (AUC) analyzes were calculated using the trapezoidal rule withbaseline subtraction (Burington, R. S., Handbook of Mathematical Tablesand Formulae, New York, McGraw-Hill, 1973). P<0.05 was considered to bestatistically significant.

Results

Effects of (Pro³)GIP on plasma glucose and insulin concentrations 4hours after administration were examined. The results are shown in FIGS.42A through 42D, which are a set of two line graphs (FIGS. 42A, 42C) andtwo bar graphs (FIGS. 42B, 42D) showing the effects of (Pro³)GIP onplasma glucose and insulin response to native GIP 4 hours afteradministration. Tests were conducted 4 hours after administration of(Pro³)GIP (25 nmoles/kg body weight) or saline (0.9% NaCl) in 18hour-fasted ob/ob mice. Plasma glucose and insulin concentrations weremeasured prior to and after i.p. administration of glucose (18 mmoles/kgbody weight) in combination with native GIP (25 nmoles/kg body weight).The incremental area under the glucose or insulin curves (AUC) between 0and 60 min are shown in the right panels. Values represent means±SEM for8 mice. *P<0.05 and **P<0.01 compared with saline alone group.

As shown in FIGS. 42A through 42D, administration of (Pro³)GIP for 4hours previously impaired the plasma glucose and insulin responses tonative GIP, given together with glucose. AUC glucose and insulin valueswere increased by 151% (P<0.05) and decreased by 25% (P<0.05);respectively, compared with saline-treated controls. This supports aprotracted biological half-life and forms the basis of the once-dailyinjection.

The effects of (Pro³)GIP on food intake, body weight and non-fastingplasma glucose and insulin concentrations were studied. The results areshown in FIGS. 43A through 43D, which are a set of two line graphs andtwo bar graphs showing the effects of daily (Pro³)GIP administration onfood intake (FIG. 43A), body weight (FIG. 43B), plasma glucose (FIG.43C) and insulin (FIG. 43D) concentrations in ob/ob mice. Parameterswere measured for 5 days prior to, 11 days during (indicated by blackbar) and 9 days after treatment with saline or (Pro³)GIP (25 nmol/kgbw/day). Values are mean±SEM for eight mice. *P<0.05 compared withsaline group.

Administration of (Pro³)GIP had no effect on food intake and body weight(FIGS. 43A and 43B). On day 11, plasma glucose had declined tosignificantly reduced (P<0.05) concentrations in ob/ob mice receiving(Pro³)GIP (FIG. 43C). Cessation of treatment returned plasma glucoseconcentrations towards control levels. Consistent with this pattern,glycated hemoglobin was significantly lower (P<0.05) after 11 daystreatment with (Pro³)GIP than either before or 9 days followingcessation of daily injection (8.0±0.3%, 6.9±0.2%, 7.7±0.4%,respectively). No significant changes in plasma insulin levels werenoted during or after the treatment period. However, there was a generaltrend for plasma insulin concentrations to decrease progressively during(Pro³)GIP treatment (FIG. 43D).

The effects of (Pro³)GIP on glucose tolerance are shown in FIGS. 44Athrough 44D, which are a set of four line graphs with inset bar graphsshowing the effects of daily (Pro³)GIP administration on glucosetolerance and plasma insulin response to glucose in ob/ob mice. Testswere conducted after daily treatment with (Pro³)GIP (25 nmoles/kg bodyweight/day; ▴; black bars) or saline (control; □; white bars) for 11days (FIG. 44A, 44C) or 9 days after cessation of treatment (FIG. 44B,44B). Glucose (18 mmoles/kg body weight) was administered at the timeindicated by the arrow. Plasma glucose (FIG. 44A, 44B) and insulin (FIG.44C, 44D) AUC values for 0-60 minutes post injection, with identicalbaseline subtractions in each case to demonstrate the complete effect of(Pro³)GIP treatment, are shown in insets. Values are mean±SEM for eightmice. *P<0.05, **P<0.01 and ***P<0.001 compared with saline group.

Daily administration of (Pro³)GIP for 11 days resulted in significantlyreduced (P<0.001) plasma glucose concentrations at 15, 30 and 60 minutesfollowing intraperitoneal glucose (FIG. 44A). This was corroborated by asignificantly decreased 0-60 minutes AUC value (FIG. 44A) which was2.1-fold reduced (P<0.01) compared to controls. Plasma insulinconcentrations were also significantly (P<0.05) reduced 15, 30 and 60minutes following intraperitoneal glucose injection in the (Pro³)GIPtreated group (FIG. 44A). AUC, 0-60 minutes values were alsosignificantly decreased (P<0.001). Interestingly, an almost identicalpattern was observed when 11 day treated ob/ob mice were administeredglucose together with native GIP (25 nmoles/kg body weight) (data notshown). This supports the view that GIP action was effectivelyantagonized in the (Pro³)GIP treated group. Discontinuation of (Pro³)GIPtreatment for 9 days (day 20 of study) resulted in almost identicalplasma glucose and insulin responses to intraperitoneal glucose (FIG.44), with lower glucose-mediated plasma insulin concentrations noted atone time point (15 minutes; P<0.05).

The effects of (Pro³)GIP on metabolic response to feeding and insulinsensitivity are shown in FIGS. 45 and 46. FIGS. 45A through 45D are aset of two line graphs (FIGS. 45A, 45C) and two bar graphs (FIGS. 45B,45D) showing the effects of daily (Pro³)GIP administration (▴; blackbars) or saline (□; white bars) on glucose (FIGS. 45A, 45B) and insulin(FIGS. 45C, 45D) responses to feeding in ob/ob mice fasted for 18 hours.Tests were conducted after daily treatment with (Pro³)GIP (25 nmol/kgbody weight/day) or saline for 11 days. The arrow indicates the time offeeding (15 minutes). AUC values for 0-105 minutes post-feeding are alsoshown. Values are mean±SEM for eight mice. *P<0.05 compared with salinegroup.

FIGS. 46A through 46D are a set of two line graphs (FIGS. 46A, 46C) andtwo bar graphs (FIGS. 46B, 46D) showing the effects of daily (Pro³)GIPadministration on insulin sensitivity in ob/ob mice. Tests wereconducted after daily treatment with (Pro³)GIP (25 nmol/kg bodyweight/day; ▾; black bars) or saline (□; white bars) for 11 days (FIG.46A, 46B) or 9 days after cessation of treatment (FIG. 46C, 46D).Insulin (50 U/kg body weight) was administered by intraperitonealinjection at the time indicated by the arrow. AUC values for 0-60minutes post-injection are also shown. Values are mean±SEM for eightmice.*P<0.05 compared with saline group.

Plasma glucose and insulin responses to 15 minutes feeding weresignificantly lowered (P<0.05) at 30 and 60 minutes in ob/ob micetreated with (Pro³)GIP for 11 days (FIG. 45). Similarly, AUC glucose andinsulin were significantly (P<0.05) decreased in (Pro³)GIP treated ob/obmice, despite similar food intakes of 0.3-0.5 g/mouse/15 minutes. Asshown in FIGS. 46A and 45B, the hypoglycemic action of insulin wassignificantly (P<0.05) augmented in terms of AUC measures and postinjection values in ob/ob mice treated with (Pro³)GIP for 11 days. Theresponses following 9 days discontinuation of (Pro³)GIP treatment weresimilar to saline treated controls (FIG. 45C, 45D).

The effects of (Pro³)GIP on pancreatic insulin and islet morphology areshown in FIGS. 47A through 47D, and 48A through 48F. FIGS. 47A through47D are a set of four bar graphs showing the effects of daily (Pro³)GIPadministration on pancreatic weight (FIG. 47A), insulin content (FIG.47B), islet number (FIG. 47C) and islet diameter (FIG. 47D) in ob/obmice. Parameters were measured after daily treatment with (Pro³)GIP (25nmol/kg body weight/day; black bars) or saline (white bars) for 11 daysand 9 days after cessation of treatment (day 20). Values are mean±SEMfor eight mice. *P<0.05 and ***P<0.001 compared with saline group. FIGS.48A through 48F are a set of two bar graphs (FIGS. 48A, 48D) and fourphotomicrographs (FIGS. 48B, 48C, 48E, 48F), showing the effects ofdaily (Pro³)GIP administration on islet size and morphology in ob/ob)mice.

(Pro³)GIP treatment had no effect on pancreatic weight (FIG. 47A).However, pancreatic insulin content was significantly (P<0.05) decreasedin ob/ob mice receiving (Pro³)GIP for 11 days compared to controls (FIG.47B). No significant differences were observed in islet number perpancreatic section (FIG. 47C), but average islet diameter was markedlyand significantly reduced (P<0.001) in (Pro³)GIP treated ob/ob mice(FIG. 47D). These effects were effectively reversed by discontinuationof (Pro³)GIP on day 20, however average islet diameter was stillsignificantly reduced (P<0.05). As shown in FIG. 48A, more detailedanalysis revealed that the reduction is islet diameter on day 11 was dueto a significant decrease (P<0.001) in the percentage of larger diameter(>0.15 mm) islets with increases in the proportion of islets with small(<0.10 mm) and medium (0.1-0.15 mm) diameters. FIG. 48D presents similaranalysis following cessation of treatment, with a significant (P<0.05)increase in the percentage of small islets still apparent.Representative images (×40 magnification) of pancreataimmunohistologically stained for insulin from 11-day (Pro³)GIP treatedob/ob mice (FIG. 48B) and saline treated controls (FIG. 48C) illustratethe dramatic changes in pancreatic islet morphology induced by (Pro³)GIPtreatment. Pancreata immunohistologically stained for insulin on day 20are also shown (FIG. 48E, 48F).

Parameters were measured after daily treatment with (Pro³)GIP (25nmol/kg body weight/day) or saline for 11 days (FIG. 48A) and 9 daysafter cessation of treatment (FIG. 48D). Proportion of islets classifiedas large (>0.15 mm) diameter, medium (0.1-0.15 mm) diameter and small(<0.1 mm) diameter are shown. Values are mean±SEM for eight mice FIGS.48B, 48C, 48E and 48F are representative images (×40 magnification) ofpancreata stained for insulin following 11 days treatment with (Pro³)GIP(FIG. 48B) or saline (FIG. 48C). Corresponding images 9 days aftercessation of treatment with (Pro³)GIP (FIG. 48E) or saline (FIG. 48F)are also shown. The arrows indicate islets.

Example 6 N-Terminally Acetylated and Ly¹⁶ and Lys³⁷-Substituted GIP

This example examines the metabolic stability, biological activity andantidiabetic potential of fatty acid derivatized N-terminally modifiedGIP analogues. These are N-AcGIP(LysPAL¹⁶) and N-AcGIP(LysPAL³⁷), whichhave an N-terminal Tyr¹ acetyl group, and a C-16 palmitate group linkedto the epsilon-amino group of the lysine at either position 16 orposition 37 of the GIP protein.

Materials and Methods

Animals. Obese diabetic (ob/ob) mice derived from the colony maintainedat Aston University, UK were used at 12-17 weeks of age. The geneticbackground and characteristics of the colony used have been outlined indetail elsewhere (Bailey, C. J. et al., 1982, Int. J. Obesity 6:11-21;Gault, V. A. et al., 2003, J. Endocrinol. 176: 133-141). Animals werehoused in an air-conditioned room at 22±2° C. with a 12 hours light: 12hours dark cycle. Drinking water and standard rodent maintenance diet(Trouw Nutrition, Cheshire, UK) were freely available. All testsolutions were administered by i.p. injection in a final volume of 5ml/kg bw. Blood was collected from the cut tip of the tail vein ofconscious mice into chilled fluoride/heparin microcentrifuge tubesimmediately prior to injection and at the times indicated in theFigures. Plasma was separated using a Beckman microcentrifuge (BeckmanInstruments, UK) at 13,000 g for 30 second and stored at −20° C. priorto glucose and insulin determinations. All animal experiments werecarried out in accordance with the UK Animals (Scientific Procedures)Act 1986. No adverse effects were observed following acute or long-termadministration of any of the peptides.

Materials. High performance liquid chromatography (HPLC) gradeacetonitrile was obtained from Rathburn (Walkersburn, UK).Trifluoroacetic acid (TFA) and trichloroacetic acid (TCA) were obtainedfrom Aldrich (Poole, Dorset, UK). DPP IV, isobutylmethylxanthine (IBMX),alpha-cyano-4-hydroxycinnamic acid, cyclic AMP and ATP were allpurchased from Sigma (Poole, Dorset, UK). Fmoc-protected amino acidswere from Calbiochem Novabiochem (Nottingham, UK). RPMI-1640 and DMEMtissue culture medium, foetal bovine serum, penicillin and streptomycinwere all purchased from Gibco (Paisley, Strathclyde, UK). Thechromatography columns used for cyclic AMP assay, Dowex AG50-WX andneutral alumina AG7 were obtained from Bio-Rad (Life Science Research,Alpha Analytical, Lame, UK). All water used in these experiments waspurified using a Milli-Q Water Purification System (Millipore, Milford,Mass., USA). All other chemicals used were of the highest purityavailable.

Synthesis, purification and characterisation of GIP and relatedanalogues. Native GIP was sequentially synthesised using standardsolid-phase Fmoc peptide chemistry (ABI 432A Peptide Synthesiser) asdescribed previously (O'Harte, F. P. M. et al., 2002, Diabetologia 45:1281-1291). N-AcGIP(LysPAL¹⁶) and N-AcGIP(LysPAL³⁷) were synthesised inthe same way as native GIP but with the exception that the epsilon-aminogroups of Lys at positions 16 or 37 were conjugated with a C-16palmitate fatty acid. In addition, an acetyl adduct was incorporated atthe N-terminal Tyr¹. The synthetic peptides were judged pure byreversed-phase HPLC on a Waters Millenium 2010 chromatography system(Software version 2.1.5) and subsequently characterised using matrixassisted laser desorption ionisation-time of flight mass spectrometry(MALDI-ToF MS) as described previously (Gault, V. A. et al., 2002, Cell.Biol. Int. 27: 41-46).

DPP IV degradation studies. GIP and fatty acid derivatised GIP analogueswere incubated at 37° C. with purified porcine dipeptidylpeptidase IV (5mU in 50 mmol/l triethanolamine-HCl; pH 7.8) for 0, 2, 4, 8 and 24 hours(final peptide concentration 2 mmol/l). The reactions were subsequentlyterminated by addition of 10% (v/v) TFA/water and the reaction productsseparated using HPLC. Reaction products were applied to a Vydac C-4column (4.6×250 mm; The Separations Group, Hesparia, Calif.) and themajor degradation product GIP(342) separated from intact GIP. The columnwas equilibrated with 0.12% (v/v) TFA/water at a flow rate of 1.0ml/minute using 0.1% (v/v) TFA in 70% acetonitrile/water with theconcentration of acetonitrile in the eluting solvent being raised from0% to 40% over 10 minutes, and then from 40% to 75% over 35 minutes. Theabsorbance was monitored at 206 nm using a SpectraSystem UV 2000Detector (Thermoquest Limited, Manchester, UK) and the peaks collectedmanually prior to MALDI-ToF MS analysis. HPLC peak area data were usedto calculate % intact peptide remaining throughout the incubation.

Cells and cell culture. Chinese hamster lung (CHL) fibroblasts stablytransfected with the human GIP receptor (Gremlich, S. et al., 1995,Diabetes 44: 1202-1208) were cultured in DMEM tissue culture mediumcontaining 10% (v/v) FBS, 1% (v/v) antibiotics (100 U/ml penicillin, 0.1mg/ml streptomycin). Clonal pancreatic BRIN-BD11 cells (McClenaghan, N.H. et al., 1996, Diabetes 45: 1132-1140) were cultured using RPMI-1640culture medium containing 10% (v/v) FBS, 1% (v/v) antibiotics (100 U/mlpenicillin, 0.1 mg/ml streptomycin) and 11.1 mmol/l glucose. Cells weremaintained at 37° C. in an atmosphere of 5% CO₂ and 95% air using anLEEC incubator (Laboratory Technical Engineering, Nottingham, UK).

In vitro biological activity. Intracellular cyclic AMP production wasmeasured using GIP-receptor transfected CHL fibroblasts (O'Harte, F. P.M. et al., 2002, Diabetologia 45: 1281-1291). In brief, CHL cells wereseeded into 12-well plates (Nünc, Roskilde, Denmark) at a density of 10⁵cells per well and allowed to grow for 48 hours before being loaded withtritiated adenine (2 μCi; TRK311; Amersham, Buckinghamshire, UK). Thecells were then incubated at 37° C. for 6 hours in 1 ml DMEMsupplemented with 0.5% (w/v) BSA and subsequently washed twice with HBSbuffer (pH 7.4). Cells were then exposed to GIP/GIP analogues (10⁻¹³ to10⁻⁶ mol/l) in HBS buffer in the presence of 1 mmol/l IBMX for 15minutes at 37° C. The medium was subsequently removed and the cellslysed with 1 ml of 5% TCA containing 0.1 mmol/l unlabelled cyclic AMPand 0.1 mmol/l unlabelled ATP. The intracellular cyclic AMP was thenseparated on Dowex and alumina exchange resins as described previously(O'Harte, F. P. M. et al., 2002, Diabetologia 45: 1281-1291).

Insulin-release studies were carried out using clonal pancreaticBRIN-BD11 cells as described previously (O'Harte, F. P. M. et al., 2002,Diabetologia 45: 1281-1291). Briefly, BRIN-BD11 cells were seeded into24-well plates at a density of 10⁵ cells per well, and allowed to attachovernight at 37° C. Acute tests for insulin release were preceded by 40minutes pre-incubation at 37° C. in 1.0 ml Krebs Ringer bicarbonatebuffer supplemented with 1.1 mmol/l glucose. Test incubations wereperformed in the presence of 5.6 mmol/l glucose with a range ofconcentrations (10⁻¹³ to 10⁻⁶ mol/l) of GIP and GIP analogues. After 20minutes incubation, the buffer was removed from each well and aliquots(200 μl) used for measurement of insulin.

Effects of N-AcGIP(LysPAL¹⁶) and N-AcGIP(LysPAL³⁷) in ob/ob mice.Metabolic and dose-response effects of GIP and N-AcGIP(LysPAL) analogues(at 6.25-25 nmoles/kg bw) following glucose administration (18 mmoles/kgbw) were examined in mice fasted for 18 hours. To evaluate long-termeffects, groups of ob/ob mice received once daily intraperitonealinjections (17:00 h) for 14 days of either saline vehicle (0.9%, w/v,NaCl), native GIP or N-AcGIP(LysPAL³⁷) (both at 12.5 nmoles/kg bodyweight/day). Food intake and body weight were recorded daily. Plasmaglucose and insulin concentrations were monitored at 2-6 day intervals.At 14 days, groups of animals were used to evaluate intraperitonealglucose tolerance (18 mmoles/kg) and insulin sensitivity (50 U/kg). In aseparate series, two experimental protocols were employed to examine thepossibility of GIP receptor desensitization after 14 days treatment.Acute metabolic effects of the usual injection of either saline, GIP orN-AcGIP(LysPAL³⁷) were monitored when administered together with glucose(18 mmoles/kg). In the second, acute effects of N-AcGIP(LysPAL³⁷) giventogether with glucose were examined in all 3 groups of mice. At the endof the 14-day treatment period, pancreatic tissues were excised formeasurement of insulin following extraction with 5 ml/g ice-cold acidethanol (75% ethanol, 2.35% H₂O, 1.5% HCl). Whole blood was taken fordetermination of glycated hemoglobin.

Biochemical analyses. Plasma glucose was assayed by an automated glucoseoxidase procedure (Stevens, J. F., 1971, Clin. Chem. Acta 32:199-201)using a Beckman Glucose Analyser II (Beckman, Galway, Ireland). Plasmainsulin was determined by dextran-charcoal RIA as described previously(Flatt, P. R. et al., 1981, Diabetologia 20: 573-577). Glycatedhemoglobin was determined using cation-exchange columns (Sigma, Poole,Dorset, UK) with measurement of absorbance (415 nm) in wash and elutingbuffers using a VersaMax microplate spectrophotometer (MolecularDevices, Wokingham, Berkshire, UK).

Statistics. Results are expressed as mean±SEM. Data were compared usingthe unpaired Student's t-test. Where appropriate, data were comparedusing repeated measures ANOVA or one-way ANOVA, followed by theStudent-Newman-Keuls post hoc test. Incremental areas under plasmaglucose and insulin curves (AUC) were calculated using acomputer-generated program employing the trapezoidal rule (Burington, R.S., 1973, Handbook of Mathematical Tables and Formulae, McGraw-Hill, NewYork) with baseline subtraction. Groups of data were considered to besignificantly different if p<0.05.

Results

Structural characterisation by MALDI-ToF MS. Following synthesis andHPLC purification, the molecular masses were obtained for GIP,N-AcGIP(LysPAL¹⁶) and N-AcGIP(LysPAL³⁷) using MALDI-ToF MS (Table 3,below). The mass-to-charge (m/z) ratio for native GIP was calculated tobe 4983.7 Da, corresponding very closely to the theoretical mass of4982.4 Da. Similarly, the m/z ratios for N-AcGIP(LysPAL¹⁶) andN-AcGIP(LysPAL³⁷) were 5268.9 Da and 5267.7 Da, respectively. Thesevalues correlate very closely to the theoretical mass (5266.1 Da),therefore, confirming the correct structures for each of the syntheticpeptides. TABLE 3 Structural characterisation of GIP and GIP analoguesby MALDI-ToF MS. Experimental Theoretical Difference Peptide M_(r) (Da)M_(r) (Da) (Da) GIP 4983.7 4982.4 1.3 N-AcGIP(LysPAL¹⁶) 5268.9 5266.12.8 N-AcGIP(LysPAL³⁷) 5267.7 5266.1 1.6

Peptide samples were mixed with matrix (alpha-cyano-4-hydroxycinnamicacid) and m/z ratio vs. relative peak intensity recorded using aVoyager-DE BioSpectrometry Workstation.

Degradation by DPP IV. Table 4, below, illustrates the % intact peptideremaining after incubation with DPP IV. Degradation of native GIP wasevident after just 2 hours with only 52±3% of the peptide remainingintact. After 8 hours incubation the native peptide was entirelydegraded to GIP(3-42). In contrast, both N-AcGIP(LysPAL¹⁶) andN-AcGIP(LysPAL³⁷) remained completely intact (no degradation fragmentevident) even after 24 hours incubation with DPP IV. TABLE 4 Percentageintact peptide remaining after incubation with DPP IV. % Intact peptideremaining after time (hours) Peptide 0 2 8 24 Native GIP 100 52 ± 3 0 0N-AcGIP(LysPAL1¹⁶) 100 100 100 100 N-AcGIP(LysPAL³⁷) 100 100 100 100

Values represent the % intact peptide remaining relative to the majordegradation product GIP(3-42) following incubation with DPP IV asdetermined from HPLC peak area data. The reactions were performed intriplicate and the means±SEM values calculated.

Changes in Cyclic AMP production. FIG. 50A shows intracellular cyclicAMP production by GIP (▴) and fatty acid derivatised GIP analoguesN-AcGIP(LysPAL¹⁶) (□) and N-AcGIP(LysPAL³⁷) (●), as determined by columnchromatography, in CHL cells stably expressing the human GIP receptor.Each experiment was performed in triplicate (n=3) and the resultsexpressed (means±SEM) as a percentage of the maximum GIP response.

A concentration-dependent (10⁻¹³ to 10⁻⁶ mol/l) increase in cyclic AMPproduction was observed with native GIP (EC₅₀ value 18.2 nmol/l) usingCHL cells transfected with the human GIP receptor (FIG. 50A). Likewise,both N-AcGIP(LysPAL¹⁶) and N-AcGIP(LysPAL³⁷) followed a similar patternof stimulation to that of native GIP with calculated EC₅₀ values of 12.1and 13.0 nmol/l, respectively. The lower EC₅₀ values for both analoguessuggest an enhanced cyclic AMP-stimulating potency.

In vitro insulin-releasing activity. FIG. 50B shows insulin-releasingactivity of glucose (5.6 mmol/l glucose; white bars), GIP (lined bars)and fatty acid derivatised GIP analogues N-AcGIP(LysPAL¹⁶) (grey bars)and N-AcGIP(LysPAL³⁷) (black bars) in the clonal pancreatic beta cellline, BRIN-BD11. After a pre-incubation (40 minutes), the effects ofvarious concentrations of peptide were tested on insulin-release duringa 20 minutes incubation. Values are means±SEM for 8 separateobservations. *p<0.05, **p<0.01, ***p<0.001 compared to control (5.6mmol/l glucose alone).

Consistent with its role as a potent insulinotropic hormone, native GIPdose-dependently stimulated insulin secretion (p<0.01 to p<0.001)compared to control (5.6 mmol/l glucose alone) (FIG. 50B). Likewise,both N-AcGIP(LysPAL 6) and N-AcGIP(LysPAL³⁷) significantly stimulatedglucose-induced insulin secretion (p<0.05 to p<0.001). On the basis ofcyclic AMP and insulin secretory data, both GIP analogues appear to beat least equipotent to the native peptide.

Metabolic effects in ob/ob mice. FIGS. 51A through 51D are a set of twoline graphs (FIGS. 51A, 51C) and two bar graphs (FIGS. 51B, 51D) showingglucose lowering effects (FIGS. 51A, 51B) and insulin-releasing activity(FIGS. 51C, 51D) of GIP and fatty acid derivatised GIP analogues in 18hour-fasted ob/ob mice. Plasma glucose and insulin concentrations weremeasured prior to and after i.p. administration of glucose alone (18mmoles/kg bw; ∘; white bars) as a control, or in combination with GIP(▴; lined bars) or GIP analogues N-AcGIP(LysPAL¹⁶) (□; grey bars) andN-AcGIP(LysPAL³⁷) (●; black bars) (25 nmoles/kg bw). The incrementalarea under the glucose or insulin curves (AUC) between 0 and 60 minutesare shown in the right panels. Values represent means±SEM for 8 mice.*p<0.05, **p<0.01, ***p<0.001 compared to glucose alone, ^(Δ)p<0.05,^(ΔΔ)p<0.01 and ^(ΔΔΔ)p<0.001 compared to native GIP, ^(γγγ)p<0.001compared with N-AcGIP(LysPAL16).

Basal blood glucose levels of the experimental groups were notsignificantly different at the start of the study (p>0.05). Afterinjection of glucose alone, plasma glucose levels increased rapidly,attaining values of 40.3±1.5 mmol/1 at 60 min. Native GIP reduced plasmaglucose at each of the time points monitored, however, this failed toreach significance in terms of overall glucose excursion as revealed bythe AUC values (FIG. 52B). Administration of N-AcGIP(LysPAL¹⁶) andN-AcGIP(LysPAL³⁷) produced a significant reduction in plasma glucose ateach time point (p<0.01 to p<0.001) and significantly lowered glucoseAUC (p<0.001 to p<0.001) when compared to glucose alone. Additionally,N-AcGIP(LysPAL¹⁶) and N-AcGIP(LysPAL³⁷) decreased the overall glucoseexcursion (p<0.05 to p<0.001) when compared to native GIP.

The corresponding plasma insulin responses are illustrated in FIGS. 51Cand 51D. After administration of glucose alone (control) the maximalrise in plasma insulin was observed at 15 minutes, which then felltowards basal levels over the remaining 45 minutes. Administration ofnative GIP significantly elevated the overall insulinotropic response(p<0.001) compared with glucose alone. When N-AcGIP(LysPAL¹⁶) orN-AcGIP(LysPAL³⁷) where administered together with glucose, a maximumplasma insulin concentration was observed at 15 minutes. Protractedbiological activity for both analogues was clearly evident from 30 to 60minutes. Glucose-mediated plasma insulin concentrations weresignificantly higher compared in both control (p<0.01 to p<0.001) andGIP-treated animals (p<0.05 to p<0.001). The corresponding AUC valuesfor N-AcGIP(LysPAL¹⁶) and N-AcGIP(LysPAL³⁷) revealed significantenhancements in overall glucose-mediated insulin release compared tonative GIP (1.5-fold and 2.3-fold, respectively; p<0.01 to p<0.001).N-AcGIP(LysPAL³⁷) was significantly more potent (1.5-fold: p<0.001) thanN-AcGIP(LysPAL¹⁶) at stimulating insulin secretion.

Dose-dependent metabolic effects in ob/ob mice. FIGS. 52A and 52Billustrate the dose-dependent antihyperglycaemic and insulinotropiceffects of GIP and the more potent analogue N-AcGIP(LysPAL³⁷) whenadministered with glucose to ob/ob mice. They are are a pair of bargraphs showing dose-dependent effects of GIP and N-AcGIP(LysPAL³⁷) inob/ob mice fasted for 18 hours. The incremental area under the curve(AUC) for glucose (FIG. 52A) and insulin (FIG. 52B) between 0 and 60minutes after i.p. administration of glucose alone (18 mmoles/kg bw;white bars) or in combination with GIP (lined bars) or N-AcGIP(LysPAL³⁷)(each at 6.25, 12.5 and 25 nmoles/kg bw; black bars). Values representmeans±SEM for 8 mice. **p<0.01 and ***p<0.001 compared to glucose alone.^(ΔΔ)p<0.01 and ^(ΔΔΔ)p<0.001 compared to native GIP at the same dose.

Data are presented as overall AUC responses for convenience. Expressedin this manner, native GIP did not significantly affect AUC glucose andinsulin at any of the doses tested. N-AcGIP(LysPAL³⁷) was substantiallymore potent than native GIP (p<0.01 to p<0.001) and exhibited prominentdose-dependent antihyperglycaemic and insulinotropic actions at alldoses administered (FIGS. 52A, 52B). Remarkably, even the lowestconcentration of N-AcGIP(LysPAL³⁷) tested (6.25 nmoles/kg) had highlysignificant antihyperglycaemic properties compared to glucose alone(p<0.001). Consistent with this observation, 6.25 nmoles/kgN-AcGIP(LysPAL³⁷) elicited a prominent insulin response (2.0-fold;p<0.01) compared to glucose alone.

Long-acting effects in ob/ob mice. The effects of daily injection ofN-AcGIP(LysPAL³⁷) for 14 days on food intake, body weight, glycatedhemoglobin and non-fasting plasma glucose and insulin concentrations ofob/ob mice are shown in FIGS. 53A through 53E, which are a set of graphsshowing the effects of daily N-AcGIP(LysPAL³⁷) (●; black bars)administration on food intake (FIG. 53A), body weight (FIG. 53B), plasmaglucose (FIG. 53C), insulin (FIG. 53D) and glycated hemoglobinN-AcGIP(LysPAL³⁷) (12.5 nmoles/kg/day) (FIG. 53E). Native GIP (12.5nmoles/kg/day; ▴; lined bars) or saline vehicle (control; □; white bars)were administered for the 14-day period indicated by the horizontalblack bar. Values are means±SEM for 8 mice. *p<0.05, **p<0.01 comparedto control. ^(ΔΔ)p<0.01 compared to native GIP.

GIP or N-AcGIP(LysPAL³⁷) had no effect on body weight or food intake(FIGS. 53A, 53B). Plasma glucose and insulin concentrations were alsounchanged by treatment with native GIP for 14 days (FIGS. 53C, 53D). Incontrast, daily injection of N-AcGIP(LysPAL³⁷) resulted in a progressivelowering of plasma glucose, resulting in significantly (p<0.05) loweredconcentrations at 14 days (FIG. 53C). At this time, glycated hemoglobinwas also significantly (p<0.01) decreased in N-AcGIP(LysPAL³⁷) treatedob/ob mice (FIG. 53E). These changes were accompanied by a tendencytowards elevated insulin concentrations, but these did not achievestatistical significance over the time frame studies (FIG. 53D).

Effects of long term treatment of ob/ob mice with N-AcGIP(LysPAL³⁷) onglucose tolerance. FIGS. 54A through 54D are a set of two line graphs(FIGS. 54A, 54C) and two bar graphs (FIGS. 54B, 54D) showing the effectsof daily N-AcGIP(LysPAL³⁷) administration on glucose tolerance (FIGS.54A, 54B) and plasma insulin response (FIGS. 54C, 54D) to glucose. Testswere conducted after 14 daily injections of either N-AcGIP(LysPAL³⁷)(12.5 nmoles/kg/day; ●; black bars), native GIP (12.5 nmoles/kg/day; ▴;lined bars) or saline vehicle (control; □; white bars). Glucose (18mmoles/kg) was administered by intraperitoneal injection at the timeindicated by the arrow. Plasma glucose and insulin AUC values for 0-60minutes post injection are shown in the right panels. Values aremeans±SEM for 8 mice. *p<0.05, **p<0.01, ***p<0.001 compared to control.^(Δ)p<0.05, ^(ΔΔ)p<0.01, ^(ΔΔΔ)p<0.001 compared to native GIP.

Consistent with effects on glycated hemoglobin, treatment of ob/ob micefor 14 days with N-AcGIP(LysPAL³⁷) resulted in a significant improvementin glucose tolerance (FIGS. 54A, 54B). Plasma glucose concentrationsthroughout the test and the overall 0-60 minutes AUC values weredecreased (p<0.01 to p<0.001). This was accompanied by increased insulinconcentrations during the latter stages (p<0.05) and a greater (p<0.01)overall AUC insulin response (FIGS. 54C, 54D). In contrast, dailyadministration of native GIP had no effect on glucose tolerance or theplasma insulin response to glucose compared with control ob/ob micereceiving saline injections for 14 days (FIG. 54).

Effects long term treatment of ob/ob mice with N-AcGIP(LysPAL37) oninsulin sensitivity, and effects of long term treatment of ob/ob micewith N-AcGIP(LysPAL³⁷) on pancreatic insulin content. FIGS. 55A through55D are a line graph and three bar graphs showing the effects of dailyN-AcGIP(LysPAL³⁷) administration on insulin sensitivity (FIGS. 55A, 55B)and pancreatic weight (FIG. 55C) and insulin content (FIG. 55D).Observations were conducted after 14 daily injections of eitherN-AcGIP(LysPAL³⁷) (12.5 nmoles/kg/day; ●; black bars), native GIP (12.5nmoles/kg/day; ▴; lined bars) or saline vehicle (control; □; whitebars). In FIG. 55A, insulin (50 U/kg) was administered byintraperitoneal injection at the time indicated by the arrow. Plasmaglucose AUC values for 0-60 minutes post injection are shown in theright panels. Values are means±SEM for 8 mice. *p<0.05, **p<0.01compared to control. ^(Δ)p<0.05, ^(ΔΔ)p<0.01 compared to native GIP.

Insulin sensitivity of the 3 groups of mice after 14 days treatment isshown in FIGS. 55A, 55B. Compared with ob/ob mice receiving dailyinjections of saline or native GIP, N-AcGIP(LysPAL³⁷) prompted asignificant improvement of insulin sensitivity. Both the individualglucose concentrations and 0-60 minutes AUC values were significantlydifferent (p<0.01) from the other two groups. In contrast, dailytreatment with native GIP did not affect the characteristic insulinresistance of ob/ob mice (FIG. 55A, 55B).

Treatment of ob/ob mice for 14 days with native GIP or N-AcGIP(LysPAL³⁷)did not affect pancreatic weight compared with saline-treated controls(FIGS. 55C, 55D). Similarly, pancreatic insulin content was similar inthe GIP and saline treated groups. However, daily administration ofN-AcGIP(LysPAL³⁷) significantly increased (p<0.01) insulin contentcompared with each of the other groups (FIGS. 55C, 55D).

Evaluation of GIP receptor desensitization after long term treatment ofob/ob mice with N-AcGIP(LysPAL³⁷). FIGS. 56A through 56D are a set oftwo line graphs (FIGS. 56A, 56C) and two bar graphs (FIGS. 56B, 56D)showing the retention of glucose lowering (FIGS. 56A, 56B) and insulinreleasing (FIGS. 56C, 56D) activity of N-AcGIP(LysPAL³⁷) and native GIPafter daily injection for 14 days. Glucose (18 mmoles/kg) wasadministered by intraperitoneal injection alone (□; white bars) or incombination with either N-AcGIP(LysPAL³⁷) (●; black bars) or native GIP(▴; lined bars) (both at 25 nmoles/kg) at the time indicated by thearrow. Plasma glucose and insulin AUC values for 0-60 minutes postinjection are shown in the right panels. Values are means±SEM for 8mice. *p<0.05, **p<0.01 compared to glucose alone. ^(Δ)p<0.05,^(ΔΔ)p<0.01 compared to native GIP. FIGS. 57A through 57D are a set oftwo line graphs (FIGS. 57A, 57C) and two bar graphs (FIGS. 57B, 57D)showing the acute glucose lowering (FIGS. 57A, 57B) and insulinreleasing (FIGS. 57C, 57D) effects of N-AcGIP(LysPAL³⁷) after 14 dailyinjections of either N-AcGIP(LysPAL37) (12.5 nmoles/kg/day; ●; blackbars), native GIP (12.5 nmoles/kg/day; ▴; lined bars) or saline vehicle(control; □; white bars). N-AcGIP(LysPAL³⁷) (25 nmoles/kg) wasadministered by intraperitoneal injection with glucose (18 mmoles/kg) atthe time indicated by the arrow. Plasma glucose and insulin AUC valuesfor 0-60 minutes post injection are shown in the right panels. Valuesare means±SEM for 8 mice. *p<0.05, **p<0.01 compared to mice receivingcontrol injections. ^(Δ)p<0.05, ^(ΔΔ)p<0.01 compared to group receivinginjections of native GIP.

As shown in FIGS. 56A through 56D, treatment of ob/ob mice withN-AcGIP(LysPAL³⁷) for 14 days did not prevent the ability of the peptideto significantly moderate the glycaemic excursion (p<0.01) and enhanceplasma insulin concentrations (p<0.01) when administered acutely withintraperitoneal glucose. In contrast, the responses of ob/ob mice toacute administration of native GIP were almost identical in micereceiving treatment with GIP or saline for 14 days (FIGS. 56A-56D). Tofurther substantiate the lack of GIP receptor desensitization followingchronic treatment with N-AcGIP(LysPAL³⁷), the acute effects of theanalogue, administered with glucose, were examined in each of the 3groups after 14 days treatment with N-AcGIP(LysPAL³⁷), native GIP orsaline (FIGS. 57A-57D). Apart from lower basal values in the formergroup, the glucose and insulin responses were identical with similar0-60 minutes AUC measures for both plasma glucose and insulinconcentrations.

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

1. A peptide analogue of GIP(1-42) (SEQ ID NO: 1), comprising at least12 amino acid residues from the N-terminal end of GIP(3-42).
 2. Apeptide analogue of GIP(1-42) (SEQ ID NO:1), comprising at least 12amino acid residues from the N-terminal end of GIP(1-42) and having anamino acid substitution at Glu³.
 3. The peptide analogue of claim 2,wherein the amino acid substituted at Glu³ is selected from the groupconsisting of: proline, hydroxyproline, lysine, tyrosine, phenylalanineand tryptophan.
 4. The peptide analogue of claim 3, wherein proline issubstituted for Glu³.
 5. The peptide analogue of claim 2, furthercomprising modification by fatty acid addition at an epsilon amino groupof at least one lysine residue.
 6. The peptide analogue of claim 5,wherein the modification is the linking of a C-16 palmitate group to theepsilon amino group of a lysine residue.
 7. The peptide analogue ofclaim 6, wherein the lysine residue is Lys¹⁶.
 8. The peptide analogue ofclaim 6, wherein the lysine residue is Lys³⁷.
 9. A peptide analogue ofGIP(1-42) (SEQ ID NO:1), comprising at least 12 amino acid residues fromthe N-terminal end of GIP(1-42), and having an amino acid modificationat amino acid residues 1, 2 or
 3. 10. The peptide analogue of claim 9,wherein the N-terminal amino acid residue is acetylated.
 11. The peptideanalogue of claim 10, further comprising modification by fatty acidaddition at an epsilon amino group of at least one lysine residue. 12.The peptide analogue of claim 11, wherein the modification is thelinking of a C-16 palmitate group to the epsilon amino group of a lysineresidue.
 13. The peptide analogue of claim 12, wherein the lysineresidue is Lys¹⁶.
 14. The peptide analogue of claim 12, wherein thelysine residue is Lys³⁷.
 15. A pharmaceutical composition comprising thepeptide analogue of claim
 2. 16. The pharmaceutical composition of claim15, further comprising a pharmaceutically acceptable carrier.
 17. Thepharmaceutical composition of claim 15, wherein the peptide analogue isin the form of a pharmaceutically acceptable salt.
 18. Thepharmaceutical composition of claim 15, wherein the peptide analogue isin the form of a pharmaceutically acceptable acid addition salt.
 19. Amethod of treating insulin resistance, the method comprisingadministering to a mammal in need of such treatment a therapeuticallyeffective amount of the composition of claim
 15. 20. A method oftreating obesity, the method comprising administering to a mammal inneed of such treatment a therapeutically effective amount of thecomposition of claim
 15. 21. A method of treating type 2 diabetes, themethod comprising administering to a mammal in need of such treatment atherapeutically effective amount of the composition of claim
 15. 22. Apeptide analogue of GIP(1-42) (SEQ ID NO: 1), wherein the analoguecomprises: a base peptide consisting of one of the following: GIP(1-12),GIP(1-13), GIP(1-14), GIP(1-15), GIP(1-16), GIP(1-17), GIP(1-18),GIP(1-19), GIP(1-20), GIP(1-21), GIP(1-22), GIP(1-23), GIP(1-24),GIP(1-25), GIP(1-26), GIP(1-27), GIP(1-28), GIP(1-29), GIP(1-30),GIP(1-31), GIP(1-32), GIP(1-33), GIP(1-34), GIP(1-35), GIP(1-36),GIP(1-37), GIP(1-38), GIP(1-39), GIP(1-40), GIP(1-41) and GIP(1-42);which possesses one or more of the following modifications: an aminoacid substitution at one or more of the residues; an amino acidsubstitution of lysine for one or more or the residues; an amino acidsubstitution at Glu³; a modification by fatty acid addition at anepsilon amino group of at least one lysine residue; and a modificationby N-terminal acetylation.
 23. The peptide analogue of claim 22, whereinthe analogue has a proline substituted for Glu³.
 24. The peptideanalogue of claims 22, further comprising modification by fatty acidaddition at an epsilon amino group of at least one lysine residue. 25.The peptide analogue of claim 24, wherein the modification is thelinking of a C-16 palmitate group to the epsilon amino group of a lysineresidue.
 26. The peptide analogue of claim 25, wherein the lysineresidue is Lys¹⁶.
 27. The peptide analogue of claim 25, wherein thelysine residue is Lys³⁷.
 28. A pharmaceutical composition comprising thepeptide analogue of claim
 22. 29. The pharmaceutical composition ofclaim 28, further comprising a pharmaceutically acceptable carrier. 30.The pharmaceutical composition of claim 28, wherein the peptide analogueis in the form of a pharmaceutically acceptable salt.
 31. Thepharmaceutical composition of claim 28, wherein the peptide analogue isin the form of a pharmaceutically acceptable acid addition salt.
 32. Amethod of treating insulin resistance, the method comprisingadministering to a mammal in need of such treatment a therapeuticallyeffective amount of the composition of claim
 28. 33. A method oftreating obesity, the method comprising administering to a mammal inneed of such treatment a therapeutically effective amount of thecomposition of claim
 28. 34. A method of treating type 2 diabetes, themethod comprising administering to a mammal in need of such treatment atherapeutically effective amount of the composition of claim
 28. 35. Apeptide analogue of GIP(1-42) (SEQ ID NO:1), comprising at least 12amino acid residues from the N-terminal end of GIP(3-42), wherein thepeptide analogue is resistant to degradation by enzyme DPP IV whencompared to naturally-occurring GIP.
 36. A peptide analogue of GIP(1-42)(SEQ ID NO:1), comprising at least 12 amino acid residues from theN-terminal end of GIP(1-42) and having an amino acid substitution atGlu³, wherein the peptide analogue is resistant to degradation by enzymeDPP IV when compared to naturally-occurring GIP.
 37. A peptide analogueof GIP(1-42) (SEQ ID NO:1), comprising at least 12 amino acid residuesfrom the N-terminal end of GIP(3-42), wherein the peptide analoguemodulates insulin secretion.
 38. A peptide analogue of GIP(1-42) (SEQ IDNO:1), comprising at least 12 amino acid residues from the N-terminalend of GIP(1-42) and having an amino acid substitution at Glu³, whereinthe peptide analogue modulates insulin secretion.